Overt and occult hepatitis B infection after neonatal vaccination: mother-to-infant transmission and HBV vaccine effectiveness.

• Overt and occult hepatitis B infections among pregnant women were still prevalent during the transition period in China. • Separation of occult hepatitis B infection from "healthy" subjects tended to increase the effectiveness estimates of current neonatal vaccination against hepatitis B virus. • Pregnant women with overt hepatitis B infection primarily transmitted the virus, which resulted in an overt or occult infection in their infants. Intensive prenatal screening of hepatitis B surface antigen for pregnant women is essential. • A high rate of loss-to-follow-up could not be ignored in this study. Overt and occult hepatitis B infection (HBI) among mothers and infants were investigated, and the effectiveness of vaccination against HBI was evaluated based on transmission types. A hospital-based cohort was built with 2,734 mothers and 330 mother-infant pairs. Their demographic data were collected. Serological HBV markers, nested-PCR for HBV genes, viral load detection, and phylogenetic analysis were done. The overall prevalence of HBI among mothers was 12.1% (330/2,734), with 10.4% for the overt type and 1.8% for the occult type. In 330 out of 1,650 (20%) mother-infant pairs, the overall, type-I (from overt mother to overt infant), type-II (from overt mother to occult infant), and type-Ⅲ (from occult mother to occult infant) transmissions were 1.9% (1/54), 5.6% (3/54) and 0.0% (0/7). The refinement of HBI classification improved the estimate of vaccine effectiveness against HBI from 74.4%–80.9% to 94.4%, which was more prominent for type-II. One mother-infant pair with type-II transmission shared nearly identical complete sequences. However, the high rate of lost-to-follow-up could not be ignored. During the transition period, HBV is mainly transmitted from the overt type of HBI mother to infant. Intensive prenatal screening for mothers is vital. [ABSTRACT FROM AUTHOR]