Immunological priming of one dose of inactivated hepatitis A vaccine given during the first year of life in presence of maternal antibodies.
BACKGROUND
In hepatitis A virus (HAV)-seronegative infants, inactivated hepatitis A vaccines are highly immunogenic. On the contrary, in infants who are HAV-seropositive before vaccination, the interfering effect of passively-transferred maternal anti-HAV antibodies leads to lower post-primary immunization anti-HAV levels, as compared to those achieved by seronegative infants. One possible way to overcome this drawback is to delay hepatitis A vaccination later during the first year of life. The objective of the study was to document the immunogenicity of an inactivated hepatitis A vaccine in 6 months old HAV-seropositive infants, given as two dose regimen consisting of a single primary immunization at 6 months of age, followed by a booster dose 6 months later.


METHODS
The immunogenicity of one hepatitis A vaccine (Avaxim pediatric, Aventis Pasteur) was documented in 108 6 months old, HAV-seropositive infants randomly assigned to receive one priming dose of hepatitis A vaccine either concomitantly with (Group 2) or 2 weeks after the third dose of routine diphteria-tetanus-whole cell pertussis reconstituting lyophilized tetanus conjugated Haemophilus influenzae type b (DTwcP//PRP approximately T) vaccine and oral poliomyelitis vaccine (OPV) (Group 1). A booster dose was given 6 months later, concomitantly with MMR vaccine.


RESULTS
The 91 infants who were HAV-seropositive (ELISA titer >20 mIU/ml) at the moment of primo vaccination remained seropositive 1 month later. Geometric mean titers (GMT) decreased from 292 and 278 mIU/ml 1 month after the first dose, to 77.6 and 76.0 mIU/ml 6 months after, in Groups 1 and 2, respectively. Post-booster titers increased markedly in both groups, with GMTs of 1731 and 1866 mIU/ml and geometric mean post/pre-immunization titer ratios of 22.3 and 24.6, respectively.


CONCLUSIONS
These results suggest that immunological priming induced by a single dose of Avaxim pediatric administered to 6 or 6.5 months old, HAV-seropositive infants is present and should not preclude the use of this vaccine in such populations.
Lagos
Rosanna
R
Centro para la Vacunas en Desarollo-Chile, Hospital Roberto del Rio, Santiago, Chile.
Munoz
Alma
A
Dumas
Rafaele
R
Pichon
Sylvie
S
Zambrano
Betzana
B
Levine
Myron
M
Vidor
Emmanuel
E
D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006506:Hepatitis A / Q000276:immunology; D035922:Hepatitis A Antibodies / Q000032:analysis / Q000096:biosynthesis; D022362:Hepatitis A Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D006801:Humans; D007112:Immunity, Maternally-Acquired / Q000276:immunology*; D007117:Immunization, Secondary; D007223:Infant; D008297:Male; D015164:Vaccines, Inactivated / Q000276:immunology
D035922:Hepatitis A Antibodies; D022362:Hepatitis A Vaccines; D015164:Vaccines, Inactivated