The immunogenicity of hepatitis B virus vaccine was studied in 38 Chinese neonates, 23 of whom were healthy and susceptible and 15 of whom had passive serum antibody to hepatitis B surface antigen (anti-HBs). Initially, each infant received two 20-µg doses of vaccine by the intramuscular route, with a one-month interval between doses. No adverse reactions occurred, and all susceptible neonates had a brisk antibody response that was comparable to that in older infants and children and superior to that in adults. The first dose of vaccine stimulated the production of anti-HBs within one month in 48% of the neonates. Anti-HBs was detectable in the serum of 91% of the vaccinees at the age of three months — that is, two months after the second dose. By the age of six months, 96% of vaccinees had detectable anti-HBs in their serum. All vaccinees developed anti-HBs after a third dose was administered at the age of seven months. High levels of anti-HBs were sustained after vaccination in infants who initially had passive antibodies.

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