Decline of hepatitis A antibodies during the first 7 months of life in full-term and preterm infants.

In a previous study we have shown that transplacental transfer of hepatitis A antibodies to preterm infants does not differ from that observed in full-term infants. This follow-up study was designed to investigate the decline of hepatitis A virus (HAV) antibodies during the first 7 months of life in full-term and preterm infants, in an endemic region for hepatitis A. Two hundred and fifty newborn infants--147 full-term and 103 preterm infants--were enrolled. Blood samples from the infants were taken at birth, and at 3 and 7 months of age. Anti-HAV titers were determined by ELISA. A concentration of > or = 1:20 mlU/ml was considered protective. Protective hepatitis A antibodies were present at birth in 48.3% of all full-term and 49.5% of all premature infants. By the age of 7 months only 13% of full-term and 21.7% of preterm infants still had protective titers. For the seropositive full-term infants the geometric mean titers (GMT) were 15,698, 6,107 and 345 at birth, 3 months and 7 months, respectively, and for preterm infants, 10,378, 2,307 and 225 at birth, 3 months and 7 months, respectively. Significant differences in GMT between preterm and full-term infants were found at birth and at 3 months of age (P < 0.05). In a region endemic for hepatitis A, low levels of anti-HAV at 7 months of age may justify trials on infant vaccination since this is the most effective way to eliminate hepatitis A from circulation.