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An objective of the study was to determine the changes in the risk of developing hepatitis A in the 30-years period and discuss the need for vaccination against HAV infection in Croatia and the city of Rijeka comparing incidence of hepatitis A between 1970-1974 and 2000-2004 periods. Hepatitis A declined in both populations and affected more prominently older population groups. Improvement of hygiene and sanitary conditions appears to have decreased hepatitis A incidence among children and adults, but only a seroepidemiological study can give more accurate data as a basis for discussion on the necessity of vaccination as a further measure in reducing hepatitis A incidence.

We report on three cases of symptomatic transmission of the L-Zagreb mumps vaccine virus from three vaccinated children to five adult contacts. The five contact cases were parents of the vaccinated children and presented with parotitis and in one case also with aseptic meningitis. The etiology of the contacts' illness was determined by viral culture, genomic sequencing, serology and epidemiological linking. Two of the vaccinated children developed vaccine associated parotitis as an adverse event three weeks following immunization. Symptoms in contact cases developed five to seven weeks after the vaccination of the children. The five contact cases, as well as the three children with adverse events recovered completely. The children had been vaccinated with MMR vaccine produced by the Institute of Immunology Zagreb, each of them with a different lot. One of the possible explanations for these adverse events is that the very low levels of wild mumps virus circulation in the last decade, combined with waning immunity in those who received one dose of vaccine or suffered from mumps in childhood, resulted in susceptible young adults and that this unique epidemiological situation allows us to detect horizontal transmission of mumps vaccine virus.