Antibody levels below traditional threshold still protect against hepatitis B in vaccinated children

A recent study published in npj Vaccines challenges the prevailing assumption that hepatitis B surface antibody (anti-HBs) levels below 10 mIU/mL signify loss of immunity in children vaccinated against hepatitis B virus (HBV). The research followed 395 children born to HBV-infected mothers over a 5.4-year period and found no cases of breakthrough HBV infection, even in those whose antibody levels fell below the traditional protective threshold.¹

At the start of the study, about 27% of children had anti-HBs antibody levels below the 10 mIU/mL threshold, which increased to 42% at follow-up, approximately 5 years later. Despite this decline, none of the 395 children, including those unboosted with low antibody levels, developed hepatitis B infection or tested positive for hepatitis B surface antigen (HBsAg). Notably, 15% of unboosted children showed increased antibody levels over time without evidence of infection, suggesting natural immune boosting from HBV exposure in this high-risk group. These results indicate that children vaccinated against HBV remain protected even when their anti-HBs levels fall below the traditionally accepted protective threshold.¹

The cohort included children with close HBV exposure due to maternal infection, monitored twice, initially at a mean age of 3.2 years and again at 8.6 years. Participants were categorized based on whether they received a hepatitis B vaccine booster after the first measurement. Researchers assessed serological markers, including anti-HBs, HBsAg, and antibody to hepatitis B core antigen (anti-HBc).¹

The study acknowledged a relatively small subset with low antibody levels, and booster decisions were parent- and physician-driven rather than randomized. Cellular immunity was not assessed, which could also contribute to long-term protection.¹

Chronic HBV infection remains a global health concern, especially due to mother-to-child transmission (MTCT). Neonatal immunoprophylaxis, involving a hepatitis B vaccine series and immunoglobulin administration shortly after birth, is the standard preventive measure. Anti-HBs levels ≥10 mIU/mL are typically considered protective, but the clinical significance of antibody levels declining below this has been uncertain.²

These findings support the notion that declining anti-HBs levels below 10 mIU/mL do not necessarily indicate loss of immunity and that routine booster vaccination may not be required, even in high-risk populations. This could influence future hepatitis B vaccination guidelines and reduce unnecessary booster administration.

By Sophia Abene

References

1.Shen, P., Xu, C., Li, T. et al. Level of antibody to hepatitis B surface antigen declined below 10 mIU/ml is still protective. npj Vaccines 10, 126 (2025). https://doi.org/10.1038/s41541-025-01188-9

2.Global Hepatitis Report 2024: Action for Access in Low- and Middle-income Countries. World Health Organization; 2024. April 9, 2024. Accessed June 24, 2025. https://www.who.int/publications/i/item/9789240091672