Ukkonen P, Pettersson R, Halonen P
Scand J Infect Dis. 1979;11(4):311-2. doi: 10.3109/inf.1979.11.issue-4.10.
Serum specimens from 191 Finnish adults were tested for antibodies to hepatitis A virus (anti-HAV). The frequency of anti-HAV increased from 8% in the age group of 20-29 years to 92% in those older than 60 years. The level of 50% was reached between 40 and 50 years.