The Vaccine-Preventable Disease laboratory/Lao Lux Laboratory (VPD/LLL) aims to conduct research on infectious diseases that are of relevance in Laos, with a focus on those that are preventable by vaccination. Since its foundation in 2011, the laboratory has been jointly operated by staff located at the Institut Pasteur du Laos and at the Luxembourg Institute of Health (LIH). The main objectives of the Vaccine-Preventable Disease laboratory are:
- To investigate the epidemiology of infectious diseases in humans and animals, with a focus on vaccine-preventable diseases
- To provide health officials with the scientific evidence required for their decisions to improve human and animal health
- To evaluate and strengthen current disease prevention and control measures, including vaccination programs
- To build high-quality and sustainable laboratory capacity
Results and recommendations are communicated to stakeholders and partners through written and oral reports, as well as policy briefs.
All Research
Our Team
Executive summary
The Vaccine-Preventable Disease laboratory/Lao Luxembourg laboratory was established in 2011, in the framework of the “Luxembourg-Laos Partnership for Research and Capacity Building in Infectious Disease Surveillance (PaReCIDS)” project. The primary objective of PaReCIDS is to conduct scientific investigations of infectious diseases that are detrimental to the health of human and animal populations in Laos, within the context of sustainable development.
The research activities of the laboratory are designed and executed in close collaboration with local partners from governmental and non-governmental organizations. The main focus of our activities is the epidemiology of vaccine-preventable infectious diseases, as well as animal and zoonotic diseases. The goal of these collaborations is to refine our studies by taking into consideration national health priorities. As a result, our studies are of importance for stakeholders in public and animal health, because they offer scientific insight into topics such as disease burden and impact of vaccination programs, and provide recommendations to optimize national health strategies.
In the course of the past four years, we expanded our research activities towards more integrated approaches. This involved developing advanced study designs to create versatile sample cohorts to better address the needs of the country. This expansion has been possible because of the growing skill set of the team and the reliable partnerships cultivated over the years.
We, for instance, continued our long-standing partnership with the National Blood Transfusion Center, operated by the Lao Red Cross. In 2024, we launched a follow-up project focusing on the prevalence of the hepatitis B virus and other transfusion-transmissible pathogens in blood donors. A total of 6,250 participants from 17 provinces were enrolled. Laboratory analysis is ongoing.
Another study focused on maternal and neonatal vaccination protection. A total of 1,600 mother-newborn pairs were enrolled from 8 different provinces, in collaboration with the provincial hospitals. Laboratory analyses estimating seroprotection against diphtheria, pertussis, tetanus, rubella, and measles were completed in 2025. Data analysis is ongoing.
Among our other ongoing studies, two hospital-based cohorts are being established, and enrolment of participants progresses as expected. The first, focusing on reasons for hospitalization in children under five in Vientiane capital, reached about 2,300 participants. The second, focused on acute hepatitis cases in 2 different hospitals of Vientiane capital, recruited about 190 participants. For both studies, the enrolment phase is expected to end beginning of 2026. Laboratory analyses for these studies are planned for 2026.
In 2025, opportunities for training were offered to the members of the VPD lab to strengthen their expertise and skill set (for details, please see section 4). Notably, Dr Khounvisith, a Lao doctoral candidate of our team, spent three months at the Swiss Tropical and Public Health Institute (Swiss TPH) finalizing her PhD thesis and preparing for her defense under the supervision of her advisors Dr Peter Odermatt, Dr Antony Black, and Dr Judith Hübschen. Additionally, Dr Hefele shared her expertise in AI tools for research with the laboratory’s scientific staff.
Plain language summary
The Vaccine-Preventable Disease laboratory (VPD lab) / Lao Lux Laboratory was founded in 2011 as part of the “Luxembourg-Laos Partnership for Research and Capacity Building in Infectious Disease Surveillance (PaReCIDS)” project. The laboratory collaborates with local partners on studies investigating infectious diseases in human and animal populations in Laos. The findings of our studies are shared with the public and animal health authorities through clear reports that contain evidence-based recommendations. During the past four years, we initiated and conducted more challenging studies and used advanced study designs.
In 2025, the laboratory made important progress in several ongoing projects. For instance, the team completed the laboratory analyses for a study investigating protection against important infectious diseases in mothers and their newborns. The team also collaborated with the Lao Red Cross to study the prevalence of the hepatitis B virus and other transfusion-transmissible pathogens in Lao blood donors from 17 provinces. Because continuous education and improvement of skills and expertise are very important components of PaReCIDS, members of the VPD lab participated in several trainings.
Projects
Investigating hepatitis B virus infection in Lao blood donors: 2025
Members of the VPD laboratory provided training in sample and data collection and sample processing practices for blood bank staff across 18 provinces, at the National Blood Transfusion Center in Vientiane (Lao Red Cross)
National Blood Transfusion Center, Lao Red Cross
Provincial Blood Transfusion Centers
As mentioned in the 2024 activity report, the objectives of this study are to estimate the prevalence of occult hepatitis B virus (HBV) infection in Lao blood donors, describe the geographical HBV genotype distribution, document the prevalence of HBsAg in recurrent donors, and assess the impact of HBV vaccination in donors born after vaccine introduction. We consider extending the investigation to other pathogens that can produce transfusion-transmitted infections, such as hepatitis D and C viruses.
Hepatitis B is endemic in Laos, and estimates show that around 8 to 10% of adults are chronically infected. The high endemicity of HBV infection is considered a leading cause of the high prevalence of chronic liver disease in the nation, such as liver cirrhosis and liver cancer. Vaccination against hepatitis B was introduced in the country in 2001; however, vaccination rates for the hepatitis B birth dose and the hepatitis B-containing vaccine remain low, at 58% and 67%, respectively.
Previous studies have shown geographic variation in HBV epidemiology among blood donors, with higher exposure and infection rates in the northern part of the country, but without any apparent explanation for this difference. Additionally, an alarmingly high prevalence of HBsAg, a marker for active infection, was detected in repeat donors. The fact that chronically infected donors seem to return for blood donation warrants a detailed investigation of current screening methods, record keeping, and donor identification practices.
HBV genotypes B and C are thought to predominate in Laos, but the rarer genotype I has also been detected. Different HBV genotypes and variants have been associated with various degrees of disease severity and resistance to antiviral treatment. Therefore, it is of public health interest to characterize HBV variants present in blood donors throughout the country.
Furthermore, a study from 2006 found that 3.9% of donated blood was HBV DNA positive while being HBsAg negative, and was therefore missed in the screening process. Such donated blood (from occult HBV-infected (OBI) donors) represents a risk of infection to transfusion recipients. Due to financial and logistical constraints, it is currently not feasible to routinely screen all donated blood with PCR, which would detect OBI.
To understand the current situation, we will investigate the prevalence of OBI in blood donors, the geographical distribution of HBV genotypes, the prevalence of HBsAg in recurrent donors, and the impact of HBV vaccination on individuals born after vaccine introduction.
A cross-sectional study is being conducted, in collaboration with the Lao National Blood Transfusion Center (NBTC), with a target sample size of 6,300 blood donors from the 17 provinces of Laos. The enrollment of participants started in 2024 and was continued at the provincial donation centers, when individuals arrived to donate blood. The blood donation center staff managed participants’ enrolment, including the informed consent and the data collection on age, sex, and risk factors.
From each participant, 5 mL of whole blood was collected. The serum was separated and stored locally at -20°C until transport to the Institut Pasteur du Laos, where the samples were then stored at -80°C. Serological markers for HBV are being tested using commercially available Enzyme-Linked Immunosorbent Assay (ELISA) kits. Samples with markers of previous HBV infection will also be tested for the presence of HBV DNA by PCR. In addition to HBV, we plan to extend the investigation to other blood-borne pathogens, including hepatitis D virus and hepatitis C virus.
The enrollment was completed in 2025, with a total of 6,250 participants. All the selected locations were included except for Phongsaly, due to the lack of blood donations during the enrolment period of the study. Overall, 39.7% of the participants were female, and the mean age was 29.3 years. Among the most frequent occupations reported were government officer (31.8%), student (28%), and military staff (9.4%). Laboratory analyses are ongoing.
The enrollment of participants was successfully finalized in 2025. Initial laboratory analysis started in 2025 and is expected to finish in 2026. Investigating the geographical distribution of HBV genotypes, the prevalence of OBI infection, the HBsAg prevalence in repeat donors, and the impact of HBV vaccination in Laos will improve our understanding of HBV epidemiology in Laos. Additionally, our results will provide valuable information for the development of tailored interventions and resource allocation.
Maternal and neonatal vaccination protection in the Lao PDR: 2025
Blood sample collection from an umbilical cord of a neonate and subsequent sample processing.
Mahosot Hospital in Vientiane
Provincial hospitals
As mentioned in the 2024 report, the objective of this study is to investigate antibody prevalence, titers, and transplacental transfer efficiency in mother-newborn pairs in different regions of Laos.
Maternal antibodies, transferred across the placenta to the unborn child, are key in the infant’s immune defense against infectious diseases during the first few weeks and months of life before vaccination starts. In Laos, the current infant vaccination schedule includes the pentavalent vaccine (diphtheria, tetanus, pertussis, hepatitis B, Haemophilus influenzae type B) administered at the ages of 6, 10, and 14 weeks, and the measles/rubella vaccine inoculated at 9-11 and 12-23 months of age. However, in Laos there are frequent outbreaks of measles, diphtheria, and other vaccine-preventable diseases. Therefore, infants can be exposed before the initiation of vaccination, a time frame when maternal antibodies should provide protection. Additionally, in many districts of Laos, there is low or incomplete vaccination coverage, which can leave infants susceptible to infection for longer periods because of the lack or early waning of maternally acquired antibodies.
The maternal antibody concentrations, along with an efficient transplacental transfer, are essential for the protection of infants during their first few weeks and months of life. This study aims to investigate the prevalence and titers of antibodies against vaccine-preventable diseases in mother–newborn pairs from different regions in Laos. Additionally, we will analyze risk factors that can impact the efficiency of transplacental antibody transfer.
The data generated in this study can be used to improve maternal and infant health in the country. The study will provide evidence-based data to the Lao Ministry of Health and the National Immunization Program.
From each participating provincial hospital, a total of 400 samples (200 from mothers and 200 from cord blood) were collected, resulting in a sample size of 1600 mother and newborn pairs. The participating hospitals are located in Vientiane Capital, Vientiane Province, Bolikhamxai, Xaisomboon, Khammouan, Louangphabang, Houaphan, and Salavan provinces (Figure 1). These locations were selected to obtain a wide geographical distribution within the country. Pregnant women admitted to the hospital for delivery were invited to the study by the hospital staff. After informed consent, a 5 mL venous blood sample was taken from each participant by a healthcare worker. Additionally, a short questionnaire was administered to the participants by the hospital staff. The questionnaire included demographic information and other relevant factors, such as vaccination and infection history. After delivery, a 5 mL blood sample was taken from the umbilical cord. The blood samples were processed for serum separation at the laboratory of the respective hospital. The serum was kept at -20°C until transfer to the Institut Pasteur du Laos, where the samples were aliquoted and stored at -80°C until testing. The samples were tested using commercially available ELISA kits (Euroimmun). The kits were used for the detection of IgG antibodies against pertussis toxin, measles virus, tetanus toxin, diphtheria toxin, and rubella virus.
Figure 1. Map of study locations colored in blue
A total of 1,600 women with 1,605 newborns were enrolled. Five women (0.3%) had twins, two in Houaphan province, two in Khammouan province, and one in Salavan province.
In total, 69.7% of mothers (n = 1,119) and 71% (n =1,139) of newborns had protective levels of anti-diphtheria toxoid IgG antibodies (≥0.1 IU/ml). Among the protected individuals, 41.2% (n = 461) of mothers and 45.6% (n= 520) of children had a long-term protection (≥ 1 IgG IU/ml). The seroprotection rate varied between provinces, from 87% and 88.5% in mothers and newborns in Vientiane province, to 53.5% and 55% in mothers and newborns from Xaisomboon province (Table 1). The distribution of antibody concentrations in each province can be found in Figure 2.
Province | Seroprotection rate in mothers | Seroprotection rate in newborns | Anti – diphtheria toxoid IgG titers in mothers | Anti – diphtheria toxoid IgG titers in newborns | ||
% | (n) | % | (n) | (IU/ml)✦ | (IU/ml)✦ | |
Bolikhamxai | 68.0 | (136) | 68.0 | (136) | 0.18 | 0.18 |
Houanphan | 58.9 | (119) | 60.4 | (122) | 0.10 | 0.11 |
Khammouan | 80.2 | (162) | 80.7 | (163) | 0.32 | 0.35 |
Louangphabang | 60.5 | (121) | 65.0 | (130) | 0.11 | 0.15 |
Salavan | 67.7 | (136) | 66.7 | (134) | 0.16 | 0.11 |
Vientiane Capital | 82.0 | (164) | 83.5 | (167) | 0.40 | 0.45 |
Vientiane | 87.0 | (174) | 88.5 | (177) | 0.50 | 0.62 |
Xaisomboon | 53.5 | (107) | 55.0 | (110) | 0.07 | 0.06 |
✦ Geometric mean concentration (GMC) Note: Positive results were defined as ≥0.1 IU of IgG antibodies/ml, borderline results (0.01-0.099 IU/ml) were classified as negative. 127 observations are censored due to a laboratory result above the upper detection limit of the assay, defined as >2 IU/ml. The values of these observations were replaced with 2.01 IU/ml in the present analysis. | ||||||
Table 1. Seroprotection rate and geometric mean concentrations of anti-diphtheria toxoid IgG antibodies in mothers and newborns by province
For rubella, 90.2% of mothers and 91.7% of children were positive (≥11 IU/ml). Bolikhamxai was the province with the lowest number of positive individuals (Table 2). The distribution of antibody concentration in every province can be found in Figure 3.
Table 2. Seroprevalence rate and geometric mean concentrations of anti-rubella antibodies in mothers and newborns by province
Province | Seroprevalence rate in mothers | Seroprevalence rate in newborns | Anti – rubella IgG titers in mothers | Anti – rubella IgG titers in newborns | ||
|---|---|---|---|---|---|---|
% | (n) | % | (n) | (IU/ml)✦ | (IU/ml)✦ | |
Bolikhamxai | 87.5 | (175) | 88.0 | (176) | 35.4 | 36.5 |
Houanphan | 87.1 | (176) | 92.1 | (186) | 34.8 | 44.2 |
Khammouan | 90.1 | (182) | 92.6 | (187) | 40.6 | 51 |
Louangphabang | 91.5 | (183) | 93.0 | (186) | 41.6 | 51.4 |
Salavan | 91.5 | (184) | 92.5 | (186) | 38.2 | 50.7 |
Vientiane Capital | 90.0 | (180) | 89.0 | (178) | 33.8 | 38.3 |
Vientiane | 92.5 | (185) | 93.0 | (186) | 40.3 | 46.7 |
Xaisomboon | 91.0 | (182) | 93.5 | (187) | 32.2 | 41.4 |
✦ Geometric mean concentration (GMC) Note: Positive results were defined as ≥11 IU of IgG antibodies/ml, borderline results (≥8 to <11 IU/ml) were classified as negative. 84 observations are censored due to a laboratory result above the upper detection limit of the assay, defined as >200 IU/ml. The values of these observations were replaced with 201 IU/ml in the present analysis. | ||||||
Overall, 12.7% of mothers have insufficient immunity against tetanus toxoid (<0.1 IU/ml), 8.1% need a booster immediately (0.1-0.5 IU/ml), and 79.2% need a booster in the next 2 to 10 years (>0.5 IU/ml). In total, 11.8% of newborns had insufficient immunity (<0.1 IU/ml), 7.2% need a booster immediately (0.1-0.5 IU/ml), and 81.1% need a booster within 2 to 10 years (>0.5 IU/ml). Vientiane capital had the highest proportion of mothers and newborns with long-term protection, and Xaisomboon had the lowest (Table 3). The distribution of antibody concentrations can be found in Figure 4. Data analysis for measles and pertussis is ongoing.
Table 3. Seroprotection rate and geometric mean concentrations of anti-tetanus toxoid antibodies in mothers and newborns by province
Province | Seroprotection rate in mothers † | Seroprotection rate in newborns † | Anti – tetanus toxoid IgG titers in mothers | Anti – tetanus toxoid IgG titers in newborns | ||
% | (n) | % | (n) | (IU/ml)✦ | (IU/ml)✦ | |
Bolikhamxai | 76.5 | 153 | 79.0 | 158 | 1.03 | 1.11 |
Houanphan | 72.3 | 146 | 74.3 | 150 | 0.78 | 0.86 |
Khammouan | 91.6 | 185 | 91.1 | 184 | 2.09 | 2.27 |
Louangphabang | 72.0 | 144 | 76.0 | 152 | 0.67 | 0.76 |
Salavan | 69.7 | 140 | 76.1 | 153 | 0.60 | 0.80 |
Vientiane Capital | 95.0 | 190 | 94.5 | 189 | 3.09 | 3.00 |
Vientiane | 92.0 | 184 | 93.5 | 187 | 2.69 | 2.93 |
Xaisomboon | 64.5 | 129 | 64.0 | 128 | 0.40 | 0.39 |
† Individuals were classified as protected when the anti-tetanus toxoid IgG antibody titer was >0.5 IU/ml ✦ Geometric mean concentration (GMC) Note: 585 observations are censored due to a laboratory result above the upper detection limit of the assay, defined as >5 IU/ml. The values of these observations were replaced with 5.1 IU/ml in the present analysis. | ||||||
The preliminary results elucidate differences between provinces in seroprotection rates against tetanus and diphtheria. We observed that antibody concentrations in cord blood tend to be higher than concentrations in mothers. Previous studies found that at 37-41 weeks of gestation, the cord blood and maternal antibody ratio is, on average, 1.5. Antibody transfer is considered efficient when the ratio between cord blood and maternal antibody concentrations is >15. Further analyses of the antibody transfer ratio and province variation concerning seroprotection rates are ongoing. The results of this study will provide essential information on the seroprotection rate in vulnerable populations against key infectious diseases, highlighting the impact of vaccination programs in various locations within the country.
Hepatitis A and E virus seroprevalence and water, sanitation, and hygiene levels in rural areas, Khammouane province, Lao People’s Democratic Republic: A cross-sectional study
Example of sources for drinking water (unprotected well) in Mahaxay district, Khammouan province, Lao PDR
- Lao Tropical and Public Health Institute
- Swiss Tropical and Public Health Institute
- Local provincial and district hospitals
The objective of the study was to investigate the current water, sanitation and hygiene (WASH) levels in rural Lao communities and their relationship to infectious diseases (Hepatitis A and E virus).
Adequate water, sanitation, and hygiene (WASH) is important for the health of individuals and communities. WASH levels are defined according to specific WHO criteria, which include improved water source, improved sanitation (toilet) facilities, and availability of handwashing facilities on premises with soap and water. In Laos, the proportion of the population using improved source drinking water and improved sanitation facilities has increased steadily over the past 30 years. Data on infectious diseases often associated with suboptimal WASH levels is scarce in the country. Furthermore, the link between WASH levels and infectious diseases in the Lao context is unknown. Understanding this association is crucial for policymakers, as it highlights the importance of WASH and supports efforts to further improve WASH standards in rural communities.
A total of 2,300 serum samples were obtained from participants residing in three districts: Nakai (349; 15%), Mahaxay (1,047; 46%), and Bualapha (904; 39%). Overall, 1,033 (45%) of the participants were male. Participants had a mean age of 32.0 years (±16.6), ranging from 5 to 87 years. Around half of the individuals were of Lao-Loum ethnicity (1,249; 54%). The educational levels varied considerably among adults: 561 (33%) reported no formal education, approximately half completed primary school, and only 39 (2%) obtained a university degree. The majority of adults reported that farming activities were their main occupation (1,534; 91%). In all participants with available data (n=2,263), the wealth index measurement was stratified into three categories: poor (754; 33%), moderate (753; 33%), and high (756; 33%). Overall, 84% of participants had access to an improved source of drinking water, 78% had an improved sanitation (improved toilet), and only 66.9% had access to basic hygiene (handwashing station with soap and water) (Table 4).
Table 4. WASH levels management
Variables | Total |
n= 2,263 n (%) | |
Water assessment level | |
Surface water | 272 (12.0) |
Unimproved | 89 (3.9) |
Improved* | 1,902 (84.0) |
Sanitation (toilet) assessment level | |
Open defecation | 497 (22.0) |
Unimproved | 0 (0.0) |
Improved** | 1,766 (78.0) |
Hygiene (handwasing station) assessment level | |
No facility | 210 (9.3) |
Limited | 540 (23.9) |
Basic | 1,513 (66.9) |
Note: * For water level assessment, ”Improved” levels include “limited”, “basic” and “safely managed”; **For sanitation level assessment, ”Improved” levels included “limited”, “basic” and “safely managed”.
In total, 1,453 (63.2%) participants were anti-HAV seropositive, and 1,323 (57.5%) participants were anti-HEV seropositive. The proportion of participants who were seropositive for anti-HAV and anti-HEV antibodies increased with age. Seropositivity for anti-HAV and anti-HEV was 6.6% and 13.1% in participants under 10 years of age, while participants older than 50 years of age had seropositivity rates of 98.8% and 90.2%, respectively, for anti-HAV and anti-HEV (Figure 5).
Compared to participants under 21 years of age, anti-HAV seroprevalence was higher among those aged 21-40 (aOR = 11.2, 95%CI = 8.7–14.5; p< 0.001) and more than 40 years (aOR = 109.4, 95%CI = 72.6–170.3; p< 0.001). Participants from Mahaxay and Bualapha districts had a significantly lower seroprevalence compared to people from Nakaiy district (aOR = 0.5, 95%CI = 0.3–0.7; p<0.001and aOR = 0.7, 95%CI = 0.5–1.0, p= 0.04, respectively). Overall, the non-Lao-Loum groups had higher odds of anti-HAV seropositivity compared to the Lao-Loum ethnic group (aOR = 1.5, 95%CI = 1.2–2.0, p= 0.001). Improved sanitation was associated with lower odds of being anti-HAV seropositive compared to open defecation (aOR = 0.6, 95% CI = 0.4–0.8; p = 0.001) (Figure 6).
For anti-HEV, participants aged 21-40 (aOR = 6.8, 95%CI = 5.4–8.7; p< 0.001) and more than 40 years (aOR = 22.7, 95% CI = 17.1–30.3; p<0.001) had a higher seroprevalence compared to participants under 21 years of age. Participants from Mahaxay district had a higher likelihood of being anti-HEV positive compared to people from Nakaiy district (aOR = 1.4, 95% CI = 1.1–1.9, p = 0.02). Females had a lower seroprevalence compared to males (aOR = 0.6, 95%CI = 0.5–0.7, p< 0.001). Improved source of water was associated with a lower likelihood of anti-HEV seropositivity compared to surface water (aOR = 0.6, 95%CI = 0.4–0.8, p = 0.002) (Figure 6).
Figure 5. Seroprevalence of anti-HAV and anti-HEV IgG by age group
Figure 6. Multivariable analysis of anti-HAV and anti-HEV IgG seroprevalence in all participants (n=2300)
A total of 1,600 women with 1,605 newborns were enrolled. Five women (0.3%) had twins, two in Houaphan province, two in Khammouan province, and one in Salavan province.
In total, 69.7% of mothers (n = 1,119) and 71% (n =1,139) of newborns had protective levels of anti-diphtheria toxoid IgG antibodies (≥0.1 IU/ml). Among the protected individuals, 41.2% (n = 461) of mothers and 45.6% (n= 520) of children had a long-term protection (≥ 1 IgG IU/ml). The seroprotection rate varied between provinces, from 87% and 88.5% in mothers and newborns in Vientiane province, to 53.5% and 55% in mothers and newborns from Xaisomboon province (Table 1). The distribution of antibody concentrations in each province can be found in Figure 2.
Province | Seroprotection rate in mothers | Seroprotection rate in newborns | Anti – diphtheria toxoid IgG titers in mothers | Anti – diphtheria toxoid IgG titers in newborns | ||
% | (n) | % | (n) | (IU/ml)✦ | (IU/ml)✦ | |
Bolikhamxai | 68.0 | (136) | 68.0 | (136) | 0.18 | 0.18 |
Houanphan | 58.9 | (119) | 60.4 | (122) | 0.10 | 0.11 |
Khammouan | 80.2 | (162) | 80.7 | (163) | 0.32 | 0.35 |
Louangphabang | 60.5 | (121) | 65.0 | (130) | 0.11 | 0.15 |
Salavan | 67.7 | (136) | 66.7 | (134) | 0.16 | 0.11 |
Vientiane Capital | 82.0 | (164) | 83.5 | (167) | 0.40 | 0.45 |
Vientiane | 87.0 | (174) | 88.5 | (177) | 0.50 | 0.62 |
Xaisomboon | 53.5 | (107) | 55.0 | (110) | 0.07 | 0.06 |
✦ Geometric mean concentration (GMC) Note: Positive results were defined as ≥0.1 IU of IgG antibodies/ml, borderline results (0.01-0.099 IU/ml) were classified as negative. 127 observations are censored due to a laboratory result above the upper detection limit of the assay, defined as >2 IU/ml. The values of these observations were replaced with 2.01 IU/ml in the present analysis. | ||||||
Table 1. Seroprotection rate and geometric mean concentrations of anti-diphtheria toxoid IgG antibodies in mothers and newborns by province
For rubella, 90.2% of mothers and 91.7% of children were positive (≥11 IU/ml). Bolikhamxai was the province with the lowest number of positive individuals (Table 2). The distribution of antibody concentration in every province can be found in Figure 3.
Table 2. Seroprevalence rate and geometric mean concentrations of anti-rubella antibodies in mothers and newborns by province
Province | Seroprevalence rate in mothers | Seroprevalence rate in newborns | Anti – rubella IgG titers in mothers | Anti – rubella IgG titers in newborns | ||
|---|---|---|---|---|---|---|
% | (n) | % | (n) | (IU/ml)✦ | (IU/ml)✦ | |
Bolikhamxai | 87.5 | (175) | 88.0 | (176) | 35.4 | 36.5 |
Houanphan | 87.1 | (176) | 92.1 | (186) | 34.8 | 44.2 |
Khammouan | 90.1 | (182) | 92.6 | (187) | 40.6 | 51 |
Louangphabang | 91.5 | (183) | 93.0 | (186) | 41.6 | 51.4 |
Salavan | 91.5 | (184) | 92.5 | (186) | 38.2 | 50.7 |
Vientiane Capital | 90.0 | (180) | 89.0 | (178) | 33.8 | 38.3 |
Vientiane | 92.5 | (185) | 93.0 | (186) | 40.3 | 46.7 |
Xaisomboon | 91.0 | (182) | 93.5 | (187) | 32.2 | 41.4 |
✦ Geometric mean concentration (GMC) Note: Positive results were defined as ≥11 IU of IgG antibodies/ml, borderline results (≥8 to <11 IU/ml) were classified as negative. 84 observations are censored due to a laboratory result above the upper detection limit of the assay, defined as >200 IU/ml. The values of these observations were replaced with 201 IU/ml in the present analysis. | ||||||
Overall, 12.7% of mothers have insufficient immunity against tetanus toxoid (<0.1 IU/ml), 8.1% need a booster immediately (0.1-0.5 IU/ml), and 79.2% need a booster in the next 2 to 10 years (>0.5 IU/ml). In total, 11.8% of newborns had insufficient immunity (<0.1 IU/ml), 7.2% need a booster immediately (0.1-0.5 IU/ml), and 81.1% need a booster within 2 to 10 years (>0.5 IU/ml). Vientiane capital had the highest proportion of mothers and newborns with long-term protection, and Xaisomboon had the lowest (Table 3). The distribution of antibody concentrations can be found in Figure 4. Data analysis for measles and pertussis is ongoing.
Table 3. Seroprotection rate and geometric mean concentrations of anti-tetanus toxoid antibodies in mothers and newborns by province
Province | Seroprotection rate in mothers † | Seroprotection rate in newborns † | Anti – tetanus toxoid IgG titers in mothers | Anti – tetanus toxoid IgG titers in newborns | ||
% | (n) | % | (n) | (IU/ml)✦ | (IU/ml)✦ | |
Bolikhamxai | 76.5 | 153 | 79.0 | 158 | 1.03 | 1.11 |
Houanphan | 72.3 | 146 | 74.3 | 150 | 0.78 | 0.86 |
Khammouan | 91.6 | 185 | 91.1 | 184 | 2.09 | 2.27 |
Louangphabang | 72.0 | 144 | 76.0 | 152 | 0.67 | 0.76 |
Salavan | 69.7 | 140 | 76.1 | 153 | 0.60 | 0.80 |
Vientiane Capital | 95.0 | 190 | 94.5 | 189 | 3.09 | 3.00 |
Vientiane | 92.0 | 184 | 93.5 | 187 | 2.69 | 2.93 |
Xaisomboon | 64.5 | 129 | 64.0 | 128 | 0.40 | 0.39 |
† Individuals were classified as protected when the anti-tetanus toxoid IgG antibody titer was >0.5 IU/ml ✦ Geometric mean concentration (GMC) Note: 585 observations are censored due to a laboratory result above the upper detection limit of the assay, defined as >5 IU/ml. The values of these observations were replaced with 5.1 IU/ml in the present analysis. | ||||||
Our results demonstrated that WASH levels in Khammouane province remain low while the seroprevalence of anti-HAV and anti-HEV IgG is high. HAV exposure was significantly associated with ethnicity, district, and sanitation level, whereas HEV exposure was linked with sex, district, and water source. Several of these risk factors could be addressed by improving WASH and raising awareness regarding fecal-oral infections and consideration of HAV vaccination.
This study was published as:
Khounvisith V, Odermatt P, Virachith S, Innoula N, Vongphachanh B, Khenkha L, et al. Hepatitis A and E Virus Seroprevalence and Water, Sanitation and Hygiene Levels in Rural Areas of Khammouane Province, Lao People’s Democratic Republic: A Cross‐Sectional Study. Journal of Medical Virology. 2025. https://doi.org/10.1002/jmv.70524
Reasons for hospitalization in children under five: 2025
Sample collection and electronic data collection by the healthcare workers of the Children’s Hospital
- Children’s Hospital, Vientiane Capital
As mentioned in the 2024 activity report, the main objective of this study is to determine the most frequent reasons for hospitalizations in children under five years of age (CUF). In addition, the following secondary objectives were defined:
- Determine the proportion of hospitalized CUF with a suspected infectious disease etiology in relation to all other causes
- Assess disease severity, using length of hospital stay as a proxy, based on clinical diagnoses
- Identify frequent hospitalization reasons other than respiratory and gastrointestinal syndromes
- Identify microorganisms associated with respiratory and gastrointestinal syndromes in hospitalized CUF
Hospital-based active surveillance is a useful approach for monitoring severe diseases within a population. In Laos, there is a lack of information on the causes of hospitalization among children under five years of age. Research has been conducted with a focus on gastrointestinal or respiratory diseases, but it has not provided a comprehensive view of the overall burden of illness. The goal of this study is to identify and describe the most common causes of hospitalization in this age group. The study is being executed in collaboration with the Children’s Hospital, a leading pediatric institution in Vientiane Capital.
In collaboration with the Children’s Hospital and during the course of two years, we aim to enroll 3,000 children under five who are admitted for hospitalization. The Children’s hospital staff manages participant enrollment, sample collection, and data collection related to the hospital stay; and VPD lab members manage the interviews of the legal guardians and the logistical efforts to ensure sample quality (Figure 7). A pooled nasal and throat swab, and a rectal swab or stool sample are collected from the participants. The stool samples are collected using a dry stool collection tube, and swab samples are collected using flocked nylon swabs in Universal Transport Medium. Samples are stored at 4ᵒC in the hospital until transport to the Institute Pasteur du Laos, where samples are aliquoted and stored at -80ᵒC until testing (Figure 7). Data is collected electronically through questionnaires using tablets provided by the VPD lab. The questionnaires include demographic information, clinical data, anthropometric measurements, and exposure history.
Figure 7. Workflow to ensure sample quality
Data and sample collection are ongoing. As of September 2025, more than 2,300 participants have been enrolled since January 2024. Around half of the participants are male (57.6%), and the median age is 13 months, ranging from 0 to 59 months. Most of the participants are residents of Vientiane Capital (74.6%) and are Tai-Kadai (Lao Loum) (79.6%) (Table 5). The healthcare workers reported gastrointestinal diseases (39.7%) and respiratory diseases (34%) as the most frequent reasons for hospitalization.
Table 5. Demographic characteristics of participants enrolled until September 2025
Variable | Total n = 2,353 |
|---|---|
Age in months | |
<6 | 485 (20.6%) |
6-11 | 507 (21.6%) |
12-23 | 694 (29.5%) |
24-35 | 340 (14.5%) |
36-47 | 201 (8.5%) |
48-59 | 124 (5.3%) |
Unknown | 2 (0.1%) |
Biological sex | |
Male | 1,355 (57.6%) |
Female | 998 (42.4%) |
Province of residence | |
Vientiane Capital | 1,756 (74.6%) |
Vientiane | 314 (13.3%) |
Xaisomboon | 54 (2.3%) |
Xaignabouly | 51 (2.2%) |
Bolikhamxai | 47 (2.0%) |
Phongsaly | 38 (1.6%) |
Other | 93 (4.0%) |
Ethnolinguistic group | |
Tai Kadai (Lao Loum) | 1,610 (79.6%) |
Mon-Khmer (Lao Theung) | 76 (3.8%) |
Hmong-Mien (Lao Soung) | 324 (16.0%) |
Chinese-Tibetan | 3 (0.1%) |
Unknown | 340 (14%) |
To date, the most frequently reported clinical diagnoses were pneumonia and gastroenteritis (Table 6). Children under 13 months were more frequently diagnosed with pneumonia (39.4%), and children 13 months old or older were diagnosed more frequently with gastroenteritis (43.2%) (Table 6).
Table 6. Frequent clinical diagnoses by age group of participants enrolled until September 2025
Clinical diagnosis at admission | 0 to 12 months old n (%) | 13 to 59 months n (%) | Overall n (%) |
|---|---|---|---|
Abscess | 8.0 (0.7%) | 21.0 (1.7%) | 29.0 (1.2%) |
Bronchiolitis/bronchitis | 7.0 (0.6%) | 6.0 (0.5%) | 13.0 (0.6%) |
Dengue fever | 16.0 (1.4%) | 27.0 (2.2%) | 43.0 (1.8%) |
Febrile convulsion | 42.0 (3.7%) | 55.0 (4.5%) | 97.0 (4.1%) |
Gastroenteritis (acute / non acute) | 407.0 (36.0%) | 528.0 (43.2%) | 935.0 (39.8%) |
Malnutrition | 8.0 (0.7%) | 1.0 (0.1%) | 9.0 (0.4%) |
Melioidosis | 3.0 (0.3%) | 4.0 (0.3%) | 7.0 (0.3%) |
Meningitis | 16.0 (1.4%) | 22.0 (1.8%) | 38.0 (1.6%) |
Pharyngitis/Tonsillitis/Stomatitis | 12.0 (1.1%) | 86.0 (7.0%) | 98.0 (4.2%) |
Pneumonia | 445.0 (39.4%) | 310.0 (25.4%) | 755.0 (32.1%) |
Sepsis | 54.0 (4.8%) | 29.0 (2.4%) | 83.0 (3.5%) |
Other (Infectious) (measles, varicella, hand foot and mouth disease, etc.) | 64.0 (5.7%) | 74.0 (6.1%) | 138.0 (5.9%) |
Other (non-infectious) (severe acute malnutrition, Kawasaki disease, drowning, etc.) | 48.0 (4.2%) | 58.0 (4.8%) | 106.0 (4.5%) |
This study will provide insight into the main reasons for hospitalization among children under five, with a focus on infectious diseases. The study will provide crucial data about the burden and nature of childhood illnesses in Laos by determining the proportion of hospitalizations due to suspected infectious diseases compared to other causes, and analyzing disease severity through the length of the hospitalization. Additionally, the results can inform healthcare policy and pediatric care strategies, aiming to improve health outcomes for Lao children.
The infective causes of acute hepatitis and jaundice amongst hospital patients: 2025
Ms. Nouna Innoula transporting and aliquoting blood samples from enrolled participants
Mahosot Hospital, Vientiane Capital
Setthathirath Hospital, Vientiane Capital
As mentioned in the 2024 report, the objectives of this study are to conduct a comprehensive, cross-sectional, hospital-based study to determine the causes of acute jaundice and hepatitis among patients in Vientiane Capital.
In Vientiane capital, two studies have investigated the causes of jaundice and hepatitis. The first, a case-control study from 1995-1996, identified leptospirosis in 21% of the cases and IgM antibodies against hepatitis A and B virus in 14% and 10% of cases, respectively. The second study, conducted between 2001 and 2004, detected hepatitis A virus in 36% of the patients and a 5% prevalence of hepatitis B and C virus. In addition to that, 13% of the participants were diagnosed with scrub typhoid, murine typhus or leptospirosis.
Since 2004, there have been no additional studies addressing the causes of hepatitis in hospital patients in the Lao PDR. Since then, substantial progress has been made in sanitation practices, blood safety, and immunization activities, which may have influenced the epidemiology of hepatitis in the country.
A cross-sectional study is being conducted in collaboration with the Mahosot and the Setthathirath Hospitals in Vientiane Capital. After informed consent and enrollment, participants are asked by the hospital staff to complete a questionnaire capturing demographic information, risk behaviors, and medical history. A second questionnaire is used to capture information on the diagnosis given by the treating physician. The data are collected electronically through REDCap, using tablets provided by the VPD lab. Digital data collection allows real-time monitoring of the data collection process for timely detection of issues and subsequent corrective actions. In addition to the interview, participants are asked to provide a venous blood sample for laboratory analysis. The collected samples are transferred on the day of collection to the Institut Pasteur du Laos, where they are processed and stored at -80°C until testing. The collected blood samples will be tested for hepatitis viruses and other relevant pathogens to identify potential etiologies relevant in the Lao context.
The study is ongoing and as of September 2025, 188 participants were enrolled. The median age of the participants is 39 years, ranging from 16 to 85 years. Most of the participants are from Vientiane Capital (61.5%) and Vientiane Province (12.8%) and male (54.8%). The majority (91%) of participants belong to the Tai-Kadai/Lao Loum ethno-linguistic group.
Among the enrolled participants, doctors reported infectious diseases as the main cause for acute hepatitis (73.9%), followed by toxic causes (18.1%) and metabolic causes (3.2%). Other reasons for acute hepatitis and inconclusive cases accounted for 4.8%.
The most common symptoms were fatigue (18.2%), loss of appetite (13.6%), fever (10.5%) and nausea (10.5%) (Figure 8). The most common risk factors reported by the patients were eating raw/undercooked foods (45.7), alcohol consumption (44.1%), contact to animals (14.4%) and contact with contaminated floodwater, soil, and mud (11.2%) (Figure 9). Nearly 16% of the patients reported having had a family member with a liver-related illness, 13.8% reported that they had used traditional medicine and 10.1% reported to use medication at the moment (Figure 10).
Less than half of the patients (40%) were admitted to the hospital. For the admitted patients, the median length of stay was 5.6 days, ranging from 1 to 19 days.
Figure 8. Reported symptoms of patients presenting with acute hepatitis
Figure 9. Exposure to risk factors reported by the patients presenting with acute hepatitis
Figure 10. Medical history as reported by patients presenting with acute hepatitis
This hospital-based study aims to fill the knowledge gap regarding the causes of acute hepatitis in Laos. Identifying the main etiologies among these patients will assist healthcare providers in the development of more effective diagnostic and treatment strategies. The results will also inform public health programs in Laos, such as the National Strategic Plan on Viral Hepatitis 2024-2030.
Assessing measles vaccination coverage over time: Socioeconomic disparities in measles vaccination before and after COVID-19 in Laos
Anouk Neven, Competence Center for Methodology and Statistics, Luxembourg Institute of Health, Strassen, Grand Duchy of Luxembourg
In the present study, we utilize MICS data from 2000 to 2023 to assess trends, inequalities, and factors associated with measles vaccination coverage in Lao PDR.
Measles is an extremely infectious disease caused by measles virus. Transmission occurs easily through the inhalation of particles from the breath, cough or sneeze of an infected person. The infection with measles virus can lead to significant health problems, complications and even death. Measles vaccination was among the first vaccines introduced in Laos with the establishment of the National Immunization Program in the 1980s. In 2017, a second dose of measles vaccine was introduced in the country5. Despite the availability of a safe vaccine, measles outbreaks continued in the country due to low vaccination coverage rates, persisting gaps in coverage and potential problems with vaccine immunogenicity.
Assessing real-life vaccination coverage rates remains difficult because there are multiple data sources that often report conflicting data. Analyzing survey-based information on vaccination can help understand sub-population trends, vaccination gaps, and the development of targeted immunization efforts. Especially household surveys, such as the Multiple Indicator Cluster Surveys (MICS), are important data sources for vaccination coverage due to their nationwide representative design.
The MICS surveys were designed by the United Nations Children’s Fund (UNICEF) to collect internationally comparable household survey data. In the Lao PDR, surveys were carried out in 1996, 2000, 2006, 2011-12, 2017 and 2023. All datasets but the earliest are freely available (https://mics.unicef.org/surveys).
Data analyses were conducted using R software. Socio-economic characteristics and measles vaccination coverage rates were estimated using the survey weights for children’s interviews that were provided with the datasets. Income-based disparities in vaccination status were assessed through several measures, such as the concentration curve, the concentration index and its derivatives. Logistic regression analyses were performed to understand factors associated with measles vaccination coverage, taking into account the sampling weights.
Overall, the vaccination coverage with the first dose of measles vaccine increased from 37.3% in 2000 to 61.8% in 2023, with the highest coverage in 2017, with 66%, based on either vaccination documents or recall. The coverage with the second measles dose reached 47.3%, based on both recall and vaccination cards. While there was an overall increase in vaccination coverage, vaccination coverage rates varied substantially between provinces. In the 2000 survey, coverage rates ranged from 8.3% in Xiengkhouang to 69.8% in Vientiane Capital (Figure 11). In 2023, the coverage rates ranged from 32.5% in Xaisomboon to 88.7% in Xaignabouly (Figure 11). Data analyses are ongoing.
Our work systematically assesses the coverage of measles vaccination across socioeconomic and geographic dimensions in Laos to identify disparities. By analyzing representative data, we aim to provide valuable information to develop targeted immunization strategies to ensure that all population groups benefit equally from the healthcare system.
Figure 21. Estimated measles vaccination coverage by province (weighted proportions) among children aged 12 to 23 months in each survey year. The dataset from 2006 did not contain a variable indicating the province and therefore, no information is shown. The number of provinces in Laos is not the same throughout the survey years. In 2006, Xaisomboon, a special zone from 1994 to 2006, was dissolved, leading to 16 provinces and 1 municipality in the 2011 data. In 2013, Xaisomboon was re-established as Xaisomboun province, leading to 17 provinces and one municipality.
Note: The maps were created in R. The shapefiles containing the administrative boundaries of Lao PDR from 2012 were obtained from the International Steering Committee for Global Mapping (retrieved from https://maps.princeton.edu/catalog/stanford-cp768st2071). The shapefiles containing the administrative boundaries of Laos in 2017 were obtained from the Humanitarian Data Exchange website (https://data.humdata.org/dataset/lao-admin-boundaries, dataset provided by the National Geographic Department of Lao PDR, 2019). Projection used: EPSG 4326 –WGS 84.
