Excellent booster response 4-6 y after a single primary dose of an inactivated hepatitis A vaccine.

We studied the immune response of an inactivated hepatitis A vaccine (Havrix 1440) given to middle-aged travellers 4-6 y after a single, primary dose. Anti-HAV antibodies in serum were checked before and 28-35 d after the booster. All 25 vaccinees showed an impressive anamnestic booster response (geometric mean titres 32 and 2993 mIU/ml before and after the booster, respectively). The study confirms experimental data indicating that I dose of inactivated hepatitis A vaccine induces a long-term proliferative T-cell response in addition to producing anti-HAV antibody. As recall memory for this vaccine is elicited several years after a single dose there is probably no need for a second vaccine dose.