Profile of Protective Anti-Hbs Antibodies among Healthy Indian Children and Adults Immunized in Infancy

Introduction: Hepatitis-B (HB) virus infection is a serious public health problem worldwide. It's almost 20 years since HB vaccination was first introduced in our National Immunization Schedule (NIS). The study aimed to determine the proportion of subjects in various age groups (children and adults) having anti-Hbs antibody levels in the seroprotective range following early infantile hepatitis-B vaccination. Material and Methods: In this cross-sectional, observational study, apparently healthy subjects from OPDs of a tertiary care hospital in Northern India, over last one-year were enrolled after taking informed consent. Institute ethics committee clearance was obtained before enrolment. Only those subjects in specified age groups (4-6, 9-12, 16-20 years) were enrolled, who had completed vaccination during infancy, including a minimum of three doses of HB vaccine, and received no other dose of HB vaccination after infancy. Serum samples of subjects were used for measuring anti-Hbs titers (quantitative), anti-Hbc, and HbsAg (qualitative) by standard commercial ELISA kits. Anti-Hbs antibody titers >10 mIU/ml WHO was considered as protective. Results: A total of 79 subjects (M:F=48:31) were enrolled from three age groups. When tested for anti-HB antibodies in these subjects aged 4-6, 9-12, and 16-20 years, 82.7%, 73.7%, and 55% had antibodies in the protective range, respectively. This gradual decline with increasing age was also noticed in GMTs, which were 33.6, 20.9, and 19.9 mIU/mL, respectively. Out of the total subjects enrolled, 16 (20.2%) developed a subclinical natural infection shown by the presence of anti-HBc antibodies. Despite the decrease in titers of anti-HBs antibodies, such individuals remain protected against clinical illness and chronic HB virus infection upon exposure to the virus, as all of them were negative for HBsAg. Discussion: Our study shows that quite a good number of subjects developed subclinical natural infection even after primary hepatitis-B vaccination in infancy. All of them were subclinical infections, which the body could clear off, as none was HBsAg positive. Despite the disappearance of anti-HBs, such immunized individuals remain protected against clinical illness and chronic HBV infection upon exposure to the virus.Experts and most available guidelines stress upon high-risk people (including HCWs) to document postvaccination serological testing of anti-HB antibodies to ensure vaccine uptake. Once they have documented evidence of immunological response to the vaccine, they don't need regular boosters for hepatitis B in the future, even if their protective titers go down, because of immunological memory and the long incubation period of HBV infection. Conclusions: Infants who received Hepatitis-B vaccination in early infancy, when they become adults, may develop a mild infection when fresh exposure occurs to the virus; however, they remain protected against clinical illness and chronic disease. Therefore, routine boosters are not required for healthy immunocompetent adults.