[Specific immunity in preschool children at high risk of infection with hepatitis A virus].

The dynamics of postinfection immunity to hepatitis A (HA) in preschool children was studied for 2 years in an area with a high activity of the epidemic process. In primary examinations by radioimmunoassay, anti-HAV were found in 82% of the subjects. The degree of the immunity intensity was found to be markedly variable: in 21% of the children the titre of anti-HAV was 1:10, in 28%-1:40, in 37%-1:160, in 14%-1:640. One year later, in the group of children with titres 1:10-1:40 the antibody level increased from 4- to 64-fold in 66% of the subjects. The rate of increase expressed in mean coefficients of antibody rise were the higher the lower the initial anti-HAV titres were. In the children with the initial titre below 1:10 this value approached 100, and anti-HAV-IgM were found in half of the examined subjects, one third of them having experienced the jaundice form of HA. The children with titres of 1:10-1:40 were found to have both manifest (14% and 11%, respectively) and asymptomatic (only anti-HAV-IgM) forms of HA. In the group of children with titres of antibody of 1:160-1:640 neither manifest HA forms nor anti-NAV-IgM could be detected. In this group the anti-HAV titre increased 4-fold or more in only 9% whereas a decrease was observed in 59% (with titre of 1:160) and in 73% (with titre of 640). No changes in anti-HAV levels were observed in 32% and 18%, respectively. Thus, the results of the study indicate that at low levels of postinfection immunity reinfection with HAV is possible and may run both manifest and asymptomatic course.