Background: Hepatitis A virus (HAV) infection is an important public health problem in low-to-middle income countries. Yet, universal vaccination against HAV is not implemented in Thailand. With improved sanitation and hygiene, the seroepidemiological pattern of HAV has changed over time. This study aimed to assess the seroprevalence of HAV and associated factors of HAV seroprotection among Thai children and adolescents.
Methods: This cross-sectional study was conducted among healthy children and adolescents aged 1-18 years who lived in Chiang Mai, Thailand. Information regarding sociodemographic and family characteristics, sanitation and hygiene, and HAV vaccination history were collected. Sera for anti-HAV IgG antibody were analyzed by chemiluminescent microparticle immunoassay, and the level of ≥1.0 S/CO defined HAV seroprotection. Logistic regression analyses were performed to identify factors associated with seroprotection against HAV. Additionally, to adjust the effect of previous HAV vaccination on seroprotection, the analysis was further stratified by participant’s vaccination history.
Results: A total of 300 eligible participants were enrolled. The median age was 8.7 (IQR: 4.8-13.5) years, 53% were male, and 61% were underweight (body mass index<18.5 kg/m2). The median number of people in participant’s bedroom was 3 (IQR: 2-4). From vaccination record booklet and/or self-reported history, 65 participants (22%) were vaccinated against HAV. Overall, 84/300 (28%) participants demonstrated seroprotection against HAV, of whom 55/65 (85%) and 29/235 (12%) were among vaccinated and unvaccinated participants (P<0.001), respectively. Geometric mean concentration (GMC) of anti-HAV IgG antibody among participants with HAV seroprotection was 6.78 (95%CI: 5.83-7.89) S/CO, which was higher among vaccinated participants compared with unvaccinated individuals (GMC: 7.96 versus 5.01 S/CO; P=0.003). The overall multivariable analysis demonstrated that previous vaccination against HAV (adjusted odds ratio [aOR]: 48.2; 95%CI: 20.5-113.5; P<0.001) and underweight (aOR: 0.4; 95%CI: 0.2-0.8; P=0.02, compared with normal weight) were associated with seroprotection against HAV. In the stratified analyses, increased number of people in participant’s bedroom (aOR: 4.9; 95%CI: 1.5-15.9; P=0.008, per one people increased) was significantly associated with HAV seroprotection among vaccinated participants, whereas underweight was marginally associated (aOR: 0.5; 95%CI: 0.2-1.2; P=0.10) among unvaccinated participants.
Conclusions: The seroprevalence of HAV antibody in Thai children and adolescents was relatively low, particularly among unvaccinated individuals. Introduction of vaccination against HAV into Thailand Expanded Program on Immunization is a crucial strategy to prevent natural infection and serious complications among these populations during their adulthood.
Key words: hepatitis A virus; hepatitis A vaccination; seroepidemiology; seroprotection; Thai youth
