Immunogenicity of two versus three injections of inactivated hepatitis A vaccine in adults.
OBJECTIVE
To investigate the immunogenicity of two versus three injections of inactivated strain CR326F-derived hepatitis A vaccine in healthy adults.


METHODS
Healthy adult volunteers (n = 105) at Utrecht University Hospital, The Netherlands, were randomly assigned to receive intramuscular injections (deltoid muscle) of 25 Units (U) at 0 and 6 months (group A, n = 53), or at 0, 2 and 6 months (group B, n = 52). Blood was drawn before and at various time points after vaccination for determination of serum antibody to hepatitis A (anti-HAV).


RESULTS
One month after the first injection, the seroconversion rates (> or = 10 mIU/ml, international units) were 88% for group A and 90% for group B. Only 2/ 103 (one in each group) showed IgM anti-HAV. One month after the second injection, seroconversion rates were 100% in both groups. At months 3, 6 and 7, anti-HAV geometric mean titers were significantly different because of the different vaccination schedules, but they were similar at months 1, 2 and 12. The anti-HAV geometric mean titer increase after the second injection was higher when the interval between the two doses was of longer duration. Anti-HAV titers of females were significantly higher than those of males and vaccinees < or = 30 years had higher titers than those > 30 years.


CONCLUSIONS
Two 25 U doses of the vaccine investigated given at 0 and 6 months, induce adequate anti-HAV titers in all adult healthy vaccinees and are as immunogenic as three doses given at 0, 2 and 6 months.
Chen
X Q
XQ
Department of Gastroenterology, University Hospital of Utrecht, The Netherlands.
Bülbül
M
M
de Gast
G C
GC
van Loon
A M
AM
Nalin
D R
DR
van Hattum
J
J
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D005260:Female; D035922:Hepatitis A Antibodies; D022362:Hepatitis A Vaccines; D017957:Hepatitis A Virus, Human / Q000276:immunology*; D006508:Hepatitis Antibodies / Q000097:blood*; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D014761:Viral Hepatitis Vaccines / Q000008:administration & dosage / Q000276:immunology*
D035922:Hepatitis A Antibodies; D022362:Hepatitis A Vaccines; D006508:Hepatitis Antibodies; D007075:Immunoglobulin M; D014761:Viral Hepatitis Vaccines