OBJECTIVES. To examine the efficacy of current hepatitis B immuno-prophylaxis and estimate the prevalence of S-mutant infections among local newborn babies.

DESIGN. Prospective study.

SETTING. Regional hospital, Hong Kong.

PATIENTS. A total of 137 newborn babies delivered between the period of November 2000 and 30 June 2001 inclusive, whose mothers were chronic hepatitis B surface antigen carriers.

RESULTS. Of the 121 infants who were followed up for 12 months, three were found to be chronic hepatitis B virus carriers, giving a vertical transmission rate of 2.5%. One (0.8%) was suspected to be infected by the S-mutant. All the three hepatitis B virus carrier babies were born to mothers with hepatitis B e antigen, but none to the eight mothers suspected to have S-mutants. Of 119 (98.3%) infants who developed hepatitis B surface antibody upon follow-up at 12 months, 35 were found to have hepatitis B e antigen at birth. All were born to hepatitis B e antigen;ndash;positive mothers. Only three of the 35 babies were found to be hepatitis B virus carriers. Most babies lost the hepatitis B e antigen by 6 months of age; only the infected babies had the antigen persisting at 1 year of age. The non-infected infants' hepatitis B e antigen is likely transplacental.

CONCLUSIONS. Our hepatitis B virus prophylaxis programme was effective at preventing perinatal infection and the non-infected infants' hepatitis B e antigen was likely transplacental.

Key words: Hepatitis B e antigens; Hepatitis B surface antigens; Hepatitis B vaccines; Infant, newborn

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