Immunogenicity of hepatitis A-inactivated vaccine administered to seronegative infants, and serological follow-up 12 months after second dose

Aim: To evaluate a) the safety and immunogenicity of anti-HAV-inactivated vaccine administered during the first year of life to anti-HAV seronegative babies, and b) the antibody persistence in a low/intermediate endemic area. Methods: After having obtained informed written consent from mothers, 92 babies were vaccinated at 4 and 10 mo of age. All babies were seronegative at birth and did not present HAV-RNA shedding in three serial stool samples taken at 1, 2 and 3 mo of age. Results: No general side effects (fever>38°C) were observed. After the first dose of vaccine, 70/82 (85.4%) babies developed anti-HAV>10 mIU/ml and 36/82 (43.9%)>20 mIU/ml. After the second dose of vaccine, all babies developed a titre>20 mIU/ml, and GMT was 877 mIU/ml. After 1 y of follow-up, the decreasing rate was similar to that reported for adult populations. Furthermore, three babies doubled the titre observed 1 mo after the second dose, indicating the possible spread of HAV even in a low/intermediate endemic area. Conclusion: Anti-HAV vaccine is safe, immunogenic and able to induce immune memory, and can be integrated into the routine infant immunization schedule during the first year of life.