[Immunity against hepatitis A in younger age groups and the basis for an immunization program].

The naturally acquired immunity to hepatitis A virus (HAV) in a sample of 305 children, aged up to 15 years, in the municipality of Ivanić-Grad amounted to 18.7%. The study was conducted in September 1989. Of those 305 children, 16.8% of the boys and 20.7% of the girls were positive. No statistically significant difference was observed with regard to sex (p < 0.01) (chi 2 = 1.4). Of the children aged up to two years, 47.4% were exposed to the hepatitis A virus. Seropositive for anti-HAV were 8.3% in the group from 2-3 years of age, 6.4% in those aged from 4-5 years, 15.9% in the group from 6-7 years of age, 6.8% in those aged from 8-9 years, 20.0% in the group from 10-11 years of age, 27.8% in those aged from 12-13 years, and 29.0% in the group from 14-15 years of age. The spread of the infection by contact was predominant, reflecting the socioeconomic standards of the studied community (p < 0.01) (chi 2 = 29.5). A relatively high prevalence of hepatitis A infection compared to that of the developed countries, the first peak immunity rates in first-graders, a low number of cases among infants aged up to 5 years (approximately 6.0%), availability of commercial vaccine, speak in favour of including hepatitis A vaccination into the obligatory community-wide immunization program. It appears that the target age for HAV vaccination would be the age of five.