Occult HBV infection in anti-HBs-positive young adults after neonatal HB vaccination.

Previous follow-up on our neonatal HB vaccination cohorts with 80,000 individuals in Qidong, China, showed significant protective efficacy of immunization against HBV infection in childhood. However, some vaccinees were found to be HBsAg negative, but anti-HBs positive and anti-HBc positive at age 10-11 years. To study this phenomenon, 2919 vaccinees at age 19-21 years were sampled from the cohort. HBsAg(-), anti-HBs(+) and anti-HBc(+) were found in 124/2919 (4.2%) of the vaccinees. HBV DNA was detectable in 81/106 sample sera by using nested PCR. The PreS-S regions of HBV were sequenced in 41 randomly sampled sera. All the HBV isolates were HBV genotype C. Twenty one isolates (21/41, 51.2%) were identical to an HBV isolated in this area (GU434374). Only 4/41 (9.8%) showed mutations at the "a" epitope and three of them were G145A. The other mutations were found outside of the "a" epitope. Most of the sera contained <10,000 HBV copies/ml. Occult HBV infection happened in the young adults with HBsAg(-), anti-HBs(+) and anti-HBc(+) status, who received neonatal vaccination in Qidong.