Seroprevalence of antibodies to hepatitis A, B and C viruses across all age groups in Chonburi Province, Thailand, 2022–2023

ABSTRACT

Viral hepatitis is a global challenge, particularly in low- and middle-income countries. The World Health Organization aims to eliminate HBV and HCV by 2030, targeting HBsAg prevalence below 0.1% in children under 5. This study analyzed sera from 1,459 participants of all ages in Chonburi province, Thailand, between October 2022 and January 2023 to assess whether this target has been met and to evaluate the seroprevalence of anti-HBs, anti-HBc, anti-hepatitis A virus (HAV), and anti-HCV in this population. Participants were healthy individuals with no immunosuppressed status. Results indicated a 0% HBsAg seroprevalence rate among children under 5, while those born before the universal immunization program had a seroprevalence rate of 5.6%. The lowest rate of anti-HBs seropositivity (anti-HBs ≥10 mIU/mL) was observed among adolescents aged 11–20 (31.7%). The anti-HBc seropositivity rate increased with age, following a pattern similar to HBsAg trends. Only a small percentage of subjects (0.3%) tested positive for anti-HCV. The seroprevalence of anti-HAV was below 20% in individuals under 40. These findings suggest that Thailand has met the regional HBsAg seroprevalence targets for children under 5 due to high HepB vaccination coverage and timely birth doses.

Plain Language Summary

We studied blood samples to learn about three viruses: hepatitis A (HAV), hepatitis B (HBV) and hepatitis C (HCV). HBV and HCV can cause long-term liver problems, while HAV can make people suddenly sick. The World Health Organization wants to get rid of HBV and HCV by 2030. One goal is to have less than 0.1% of children under 5 with HBV. We studied blood samples from 1,459 people in Chonburi province, Thailand, to see if this goal is being met. The results were promising: no children under 5 had HBV due to vaccines given at birth. A very small number of people (0.3%) had HCV. For HAV, fewer than 20% of people under 40 had protection, meaning many could still get sick. This study shows that Thailand’s vaccine programs are working well for HBV in young children.

Introduction

In 2016, the World Health Organization (WHO) South-East Asia Regional Action Plan targeted reducing hepatitis B surface antigen (HBsAg) prevalence to < 0.1% among 5-year-old children by 2030.¹ Achieving this requires universal timely (<24 hours) hepatitis B (HepB) birth doses, HepB immunoglobulin (HBIg) for exposed neonates, and a complete HepB vaccine schedule to prevent HBV transmission. Thailand introduced HepB vaccination into the Expanded Program on Immunization (EPI) in 1988, initially in Chiang Mai and Chonburi provinces, expanding nationwide by 1992.^2,3 The original regimen included a monovalent vaccine given within 24 hours of birth and at 2 and 6 months, alongside the diphtheria-tetanus-whole-cell pertussis (DTwP) vaccine at separate sites. Since 2019, the strategy includes a monovalent HepB vaccine at birth and a pentavalent DTwP-HepB-Haemophilus influenzae type b (DTwP-HB-Hib) vaccine at 2, 4, and 6 months, with an additional HepB dose at 1 month for infants born to HBsAg-positive mothers.^4,5 Studies on impact of universal HepB vaccination in 1999, 2004, and 2014 showed the program’s success in reducing HBV transmission, with the 2014 serological survey reporting the HBV carrier rate of 0.1% in children under 5 years.^3,6,7 However, no data since 2014 has monitored whether this declining trend continues.

Similar to HBV, Hepatitis C virus (HCV) infection is a global public health concern targeted for elimination by 2030 under the WHO Global Health Sector Strategy on Hepatitis (2022–2030).⁸ In Thailand, national surveys show a decline in anti-HCV seroprevalence from 2.15% in 2004 to 0.94% in 2014, alongside a reduction in HCV viremia.^9,10 This progress is linked to shifts from intravenous to oral drug use, increased HIV awareness, improved HCV screening in blood donations, and other precautions against blood-borne pathogens. However, provinces like Phetchabun still report high anti-HCV seroprevalence (15.5%) and viremia (12.2%).¹¹ To meet its 2030 elimination goal, Thailand is piloting a decentralized test-and-treat model in Phetchabun, with potential for nationwide expansion.¹²

HBV and HCV infections, which can cause cirrhosis and hepatocellular cancer, are the focus of viral hepatitis elimination efforts as they account for 96% of hepatitis-related deaths. In contrast, Hepatitis A virus (HAV) causes acute, self-limited illness with symptoms like fever, jaundice, and nausea, lasting under two months in most cases.¹³ However, 10–15% of cases may experience prolonged or relapsing symptoms for up to six months.¹³ While 70% of children under six are asymptomatic, older children and adults are typically symptomatic.¹⁴ Improved sanitation and socio-economic conditions have significantly reduced HAV transmission in Thailand, where seroprevalence dropped from 86.4% in 1972 to 34.5% in 2014.^15,16 By 2014, 50% of the population became seropositive at age 42, compared to 4.5 years in the 1970s, indicating increased HAV susceptibility among children and young adults. Despite the availability of hepatitis A vaccines for purchase, Thailand has not included them in its EPI, as a 2002 cost-effectiveness study found insufficient benefit.¹⁷ Updated data on HAV seroprevalence, vaccine costs, and incidence, especially post-COVID-19, are needed to reassess the cost-effectiveness of hepatitis A vaccination and guide policymakers to reconsider its implementation.

The aim of the present study is to assess the current seroprevalence of hepatitis A, B, and C across all age groups in Chonburi province, Thailand using serum samples collected between October 2022 and January 2023 as part of an investigation into population immunity to COVID-19.¹⁸ The findings will provide updated serologic data to strengthen surveillance and disease control efforts to support the elimination of HBV and HCV and help to mitigate potential HAV outbreaks.

Methods

Study design and participants

The descriptive cross-sectional serosurvey study was conducted in 11 districts of Chonburi province, Thailand, from 1 October 2022 to 31 January 2023. Clusters were divided into urban and rural strata, and clusters were selected using probability-proportionate-to-size sampling. This study was part of a larger project assessing the prevalence of SARS-CoV-2 in Thailand.¹⁸ Chonburi, located 90 km from Bangkok, was chosen for its diverse landscape, including urban areas, tourist hubs like Pattaya City, industrial estates, and rural agricultural regions. This study included 1459 healthy participants aged 1 month to 80 years who reported no immunosuppression, malignancy, or severe hematologic disorders on a self-administered questionnaire.

The protocol was reviewed and approved by the Institutional Review Board of Chonburi Provincial Public Health Office (IRB no. CBO Rec 65–0024) and the Institutional Review Board of the Faculty of Medicine, Chulalongkorn University (IRB no. 0706/65 CoA No. 0066/2023). This research study was conducted in accordance with the Declaration of Helsinki and the principles of good clinical practice. All participants or their parents were informed about the study’s objectives, and written consent was obtained prior to their enrollment in the study.

Sample collection

Blood samples (3–5 mL) were collected at the study site in Chonburi province between 1 October 2022 and 31 January 2023. The blood samples underwent centrifugation to obtain serum samples, which were then aliquoted and stored at −20°C until laboratory testing. Subsequently, the samples were transported to the virology laboratory at the Center of Excellence in Clinical Virology, Faculty of Medicine, Chulalongkorn University in Bangkok for serological testing.

Serological assays

Participants’ sera samples were tested for the following five markers using an automated chemiluminescent microparticle immunoassay (CMIA) performed on the ARCHITECT system (Abbott, Wiesbaden, Germany); anti-HAV, HBsAg, anti-hepatitis B core antigen (anti-HBc), anti-hepatitis B surface antigen (anti-HBs), and anti-HCV. For anti-HAV, results were measured in relative light units (RLUs), with a seropositive cutoff value set at ≥ 1 sample to cutoff ratio (S/CO). For hepatitis B virus markers, HBsAg and anti-HBc were measured in RLUs, with a cutoff of ≥ 1 S/CO for seropositivity. Additionally, anti-HBs levels were measured quantitatively, with a threshold of ≥ 10 mIU/mL considered seroprotective against hepatitis B virus infection. Finally, anti-HCV detection was measured in RLUs, with a seropositive cutoff set at ≥ 1 S/CO.

Statistical analysis

The sample size of 1,459 individuals was calculated based on a previous study on the seroprevalence of immunity to SARS-CoV-2.¹⁸ The sample size for the HAV seroprevalence was calculated based on the prevalence reported in a previous study,¹⁶ which was 34.5%. Using a confidence level of 95% and a margin of error of 3.6%, the required sample size was determined to be 650 participants. The 650 participants randomly selected for seroprevalence study of HAV antibodies were a subset of the 1459 individuals. Data on the seropositivity rate are presented as numbers and percentages. The geometric mean titers (GMT) were calculated. Associations between HBsAg and anti-HBc seropositivity status and age groups (born before versus after EPI implementation) were analyzed using Pearson’s chi-square test. Figures were generated using GraphPad Prism v9.4.1 (GraphPad Software, San Diego, CA). A p-value of < 0.05 was considered to be statistically significant.

Results

Demographic characteristics of study participants

A total of 1,459 serum samples were evaluated between October 2022 and January 2023. The survey was conducted across 11 districts in Chonburi province, with the number of blood samples collected detailed in a previously published study.¹⁸ Participants ranged in age from 4 months to 79 years, comprising 650 men and 809 women. The mean age of participants was 33.0 years (standard deviation [SD] = 18.8), with a median age of 32.0 years (interquartile range: 16–48 years). The age groups of participants were categorized as follows: <5 years, 5–10 years, 11–20 years, 21–30 years, 31–40 years, 41–50 years, 51–60 years, 61–70 years, and >70 years. The largest age group was 21–30 years, accounting for 255 individuals (17.5%). Among the participants, 29.4% were children and adolescents (0–20 years), 63.1% were adults (21–60 years), and 7.5% were elderly individuals (>60 years). Of the 1,459 participants, 266 (18.2%) were healthcare workers (59 men and 207 women), while the remaining 1,193 (81.8%) were members of the general population (591 men and 602 women). The full demographic data of the participants was previously published.¹⁸

Seroprevalence of viral hepatitis A, B, and C

The overall seroprevalence of anti-HAV was 31.5% (205/650). Anti-HAV seropositivity increased with age, starting from 8.6% among children <5 years and increased to > 90% in individuals aged 60 and above, as illustrated in Figure 1a. The seroprevalence of anti-HAV was below 20% in individuals under 40, suggesting a lack of immunity in children and young adults. The age at midpoint of population immunity for HAV was determined using the seroprevalence curve as described in our previous publication.¹⁶ This curve depicts the percentage of individuals exhibiting anti-HAV seropositivity plotted against their respective age groups. The age at midpoint of population immunity corresponds to the age at which 50% of the population were seropositive. In this study, as illustrated in Figure 1a, it was found to be approximately 52 years.

Figure 1.

Age-stratified seroprevalence of (a) anti-hepatitis A virus (anti-HAV), (b) HBsAg, (c) anti-HBc, and (d) anti-HBs in Chonburi province, Thailand (2022–2023). In fig (a), the dashed horizontal line denotes 50% anti-HAV seropositivity rate. Intersection between the seroprevalence curve and the 50% dashed horizontal line indicates the age at which 50% of the individuals in the population possessed anti-HAV. For panel (d), the left y-axis represents the seropositivity rate, while the right y-axis represents the geometric mean titer (GMT), with means shown as red circles. The numbers above the red circles indicate GMT values (mIU/mL). For panel (a-d), the numbers above the graph represent the sample size for each age group.

The prevalence of HBsAg is 0% in individuals younger than 10 years, reflecting the impact of the universal hepatitis B vaccination program initiated within the EPI in 1988. HBsAg seroprevalence increases to 0.46% in individuals aged 11–20 and peaks at 5.88% in those aged 51–60 years and over 70 years. Overall, the seroprevalence of HBsAg was 5.6% in individuals born before the implementation of the EPI and 0.6% in those born after (p < .001), as shown in Figure 1b. This pattern aligns with the prevalence of anti-HBc, a marker of past or current HBV infection, which also demonstrates an age-related increase. Anti-HBc seroprevalence is below 2% in individuals younger than 20 years but rises sharply from 23.4% in those aged 31–40 to 88.2% in individuals older than 70 years. Similarly, the overall anti-HBc seroprevalence was 39.8% in individuals born before the EPI and 3.0% in those born after the EPI (p < .001), as shown in Figure 1c. The low seroprevalence of HBsAg and anti-HBc in children and adults born after the EPI highlights the program’s success in reducing HBV transmission.

The highest hepatitis B seroprotection rate, defined as anti-HBs ≥10 mIU/mL, is observed in children under 5 years (85.4%), with a gradual decline in seroprotection rate as age increases, as shown in Table 1. Individuals aged 5–10 years had a seroprotection rate of 56.5%, but the rate drops significantly in those aged 11–20 years (31.7%) and remains below 50% in most older age groups. However, individuals older than 70 years show a slight increase in seroprotection rate to 58.8%, likely influenced by past natural infection, as depicted in Figure 1d. The GMT shows a similar pattern, peaking in children under 5 years and declining in older age groups, with a slight increase after 70 years.

Table 1.

Anti-HBs seroprotection rates stratified by age group in Chonburi, Thailand.

	Anti-HBs seroprotection rate, N (%)		Total
Age	below 10 mIU/mL	above 10 mIU/mL
<5 years	14 (14.6%)	82 (85.4%)	96
5–10 years	50 (43.5%)	65 (56.5%)	115
11–20 years	149 (68.3%)	69 (31.7%)	218
21–30 years	159 (62.4%)	96 (37.6%)	255
31–40 years	125 (53.2%)	110 (46.8%)	235
41–50 years	124 (54.6%)	103 (45.4%)	227
51–60 years	104 (51.0%)	100 (49.0%)	204
61–70 years	50 (54.3%)	42 (45.7%)	92
>70 years	7 (41.2%)	10 (58.8%)	17
Total	782 (53.6%)	677 (46.4%)	1459

The anti-HCV seropositive rate of 0.3% (4/1459) was observed among all participants, as detailed in Table 2. Using the estimated population data for Chonburi province in 2022,¹⁹ the predicted number of anti-HCV positive individuals was calculated for different age groups. Among adults aged 21–30 years, the predicted number was 899, while for those aged 51–60 years, it was higher at 2,126 individuals. For the 61–70 age group, the predicted number was 1,422 individuals. Overall, the total predicted number of anti-HCV positive individuals is 4,447, with all cases occurring in adults aged over 20 years. This finding highlights the concentration of anti-HCV positivity in the adult population, reflecting the likely exposure risk and epidemiological trends in these age groups.

Table 2.

The approximate number of anti-HCV positive individuals stratified by age in Chonburi population.

Age group, years	Sample size	Number of anti-HCV seropositive samples	Population in Chonburiδ	Number of anti-HCV positive individuals (predict)
<5	96	0	80692	0
5–10	115	0	125258	0
11–20	218	0	199201	0
21–30	255	1	229333	899
31–40	235	0	251349	0
41–50	227	0	267013	0
51–60	204	2	216941	2126
61–70	92	1	130895	1422
>70	17	0	94076	0
Total	1459	4	1594758	4447

§Based on the actual census count in December 2022. Data available from reference 19. https://stat.bora.dopa.go.th/new_stat/webPage/statByProvince.php?year=66.

Discussion

The study demonstrated a significant decline in population immunity to HAV, with the age at the midpoint of population immunity increasing over time: from 12.49 years in 1990 to 36.02 years in 2004, 42.03 years in 2014, and 52 years in this 2022 serological survey conducted in Chonburi.^16,20 Thailand has transitioned to a low HAV endemicity status, with a substantial proportion of the population lacking immunity, particularly among adult groups. Although no significant outbreaks have occurred in recent decades, the risk of future outbreaks persists, especially from imported cases. To prevent future HAV transmission and manage public health risks, enhanced surveillance and targeted vaccination strategies are essential.

In low-income countries, HAV remains endemic. For example, a serological survey conducted in Southern Iran revealed that 81.5% of individuals aged 0–25 years were seropositive for anti-HAV.²¹ However, improved water and sanitation systems are reducing transmission rates among young children in low-income countries.²² In high-income countries, most adults remain susceptible to HAV, leading to an increase in foodborne outbreaks.^23,24 The future epidemiology of HAV will be profoundly influenced by globalization processes. These dynamics underscore the importance of implementing vaccination policies and public health surveillance strategies that are tailored to the levels of endemicity and regional socioeconomic conditions.

Efforts to combat hepatitis B in Thailand began with the introduction of a universal hepatitis B immunization program in 1988 to prevent mother-to-child transmission. These measures have significantly reduced hepatitis B prevalence among children under five.³ This study demonstrated sustained success in reducing the HBV carrier rate (HBsAg seroprevalence) in children <20 years to 0%, and the overall seroprevalence to 2.9%. This finding is in line with the studies on national HBV carrier rates showing a decline from 4.0% in 2004⁷ to 1.6% in 2014.³ Similar successes were observed in Taiwan, where universal vaccination drastically reduced childhood hepatitis B infections, HBV carrier rates, and liver cancer incidence in individuals born after the implementation of universal HepB vaccination program.²⁵

The anti-HBc seroprevalence rate in this study was comparable to the rate reported in 2014.³ From the previous national seroprevalence survey in 2014, the anti-HBc seropositivity rate was 34.5% in individuals born before the EPI began, compared to 2.3% in individuals born after EPI implementation. In this study, the anti-HBc seroprevalence was 39.8% in individuals born before the EPI and 3.0% in those born after. The pattern of anti-HBs seropositivity rates in this study was also similar to the 2004 and 2014 serosurveys,^3,7 with the highest hepatitis B seroprotection rate observed in children under five years old due to recent vaccination, followed by a gradual decline in seroprotection rates with increasing age. Our previous 20-year follow-up study of Thai infants vaccinated against HBV during infancy also demonstrated a decline in anti-HBs seroprotection rate over time, with 44.0% (11/25; 95% CI: 24.4–65.1) maintaining levels ≥ 10 mIU/mL at year 20.²⁶ However, a robust anamnestic response (93.1%) to a subsequent challenge dose indicated persistent immune memory.²⁶ A 30-year follow-up study of Alaska Native individuals showed that 51% retained protective anti-HBs levels at 30 years.²⁷ Among participants with anti-HBs levels below 10 mIU/mL, 88% responded to a booster dose, suggesting that vaccinated individuals remain protected against chronic HBV infection for up to 30 years after childhood vaccination.²⁷

This study also investigated the current seroprevalence of anti-HCV. The prevalence found in this study was 0.3% and was not found among children or teenagers. These results align with the remarkable decline in anti-HCV prevalence in Thailand, which decreased from 2.15% in 2004⁹ to 0.94% in 2014.¹⁰ In 2014, the large-scale serological survey in Thailand showed that anti-HCV seropositive rates peaked in individuals aged 41–50 years, and it was estimated that 759,000 Thai individuals were anti-HCV-positive, and 357,000 Thai individuals had viremic HCV infection, representing a significant burden.¹⁰ Globally, the burden of HCV has declined due to the effectiveness of preventive measures such as enhanced blood screening protocols, reductions in high-risk behaviors, and the implementation of universal precautions.²⁸ Nevertheless, HCV prevalence and burden were found to be significantly higher among HIV-infected individuals compared to HIV-negative individuals and among people who inject drugs (PWID).²⁹ Therefore, routine HCV testing in all HIV-infected individuals and PWID, coupled with improved country-level surveillance of HCV prevalence across diverse population groups, is critical for achieving the HCV elimination goal by 2030.

This study has several limitations. First, it focuses on a single province, underscoring the need to sample a broader population across the four regions of Thailand. Second, the study’s inclusion criteria excluded high-risk groups such as prisoners, PWID, and individuals with chronic illnesses or HIV. Therefore, our findings cannot be extrapolated to this population. Finally, the historical Thai data used for comparison also excluded high-risk groups. Further research targeting these populations is essential to accurately determine the true burden of hepatitis A, B and C and to develop comprehensive elimination strategies.

Thailand’s ongoing efforts in hepatitis B and C screening, vaccination, and treatment have significantly reduced infection rates. However, targeted studies and interventions in high-risk populations remain crucial to ensuring the success of these elimination initiatives. With sustained commitment, the country is on track to achieve the WHO’s hepatitis elimination goals by 2030.

Biographies

Nasamon Wanlapakorn is an Associate Professor of Pediatrics at the Faculty of Medicine, Chulalongkorn University, and specializes in vaccine immunology, clinical virology and seroepidemiology of viral diseases.

Jira Chansaenroj is a post-doctoral researcher at the Center of Excellence in Clinical Virology at the Faculty of Medicine, Chulalongkorn University. His research interests are virology, molecular biology, and seroepidemiology of infectious diseases.

Preeyaporn Vichaiwattana is a senior research scientist at the Center of Excellence in Clinical Virology, Faculty of Medicine, Chulalongkorn University. She specializes in ELISA, PCR, and other related molecular biology lab techniques.

Sirapa Klinfueng is a research scientist at the Center of Excellence in Clinical Virology, Faculty of Medicine, Chulalongkorn University. She specializes in ELISA, PCR, cell culture and other related molecular techniques in virology and immunology.

Yong Poovorawan is a Professor of Pediatrics at the Faculty of Medicine, Chulalongkorn University, and currently the director of the Center of Excellence in Clinical Virology at the Faculty of Medicine, Chulalongkorn University. He specializes in hepatology, virology, molecular biology, epidemiology, and emerging infectious diseases.

Funding Statement

This research was financially supported by the Health Systems Research Institute (HSRI), the National Research Council of Thailand (NRCT), the Center of Excellence in Clinical Virology, Chulalongkorn University, and King Chulalongkorn Memorial Hospital, and the Second Century Fund (C2F) of Jira Chansaenroj, Chulalongkorn University. The funders had no role in the study design, data collection, analysis, publication decision, or manuscript preparation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions statement

Conceptualization: NW

Data curation: NW, JC, PV

Formal Analysis: NW, JC

Acquisition: NW, YP

Investigation: JC, SK, PV

Supervision: NW, YP

Writing-Original draft: NW

Writing-Review and Editing: NW, YP

Data availability statement

Data will be made available upon request.

Declaration of generative AI and AI-assisted technologies in the writing process

We would like to declare that generative AI (ChatGPT-3.5) was used solely for assistance in checking and refining the English language in this manuscript. The content, ideas, and findings presented in the manuscript were entirely generated by the authors without AI assistance. After language editing, the final version was reviewed and validated by the authors to ensure its accuracy and integrity.

Ethics statement

The protocol was reviewed and approved by the Institutional Review Board of Chonburi Provincial Public Health Office (IRB no. 0024–2565) and the Institutional Review Board of the Faculty of Medicine, Chulalongkorn University (IRB no. 0706/65 CoA No. 0066/2023).

Informed consent statement

Informed consent and/or assent was obtained before participant enrollment. The study was conducted according to the Declaration of Helsinki and the Good Clinical Practice Guidelines (ICH-GCP) principles.