Horizontal transmission of the Leningrad-Zagreb mumps vaccine strain: a report of six symptomatic cases of parotitis and one case of meningitis.

Here we report horizontal symptomatic transmission of the Leningrad-Zagreb (L-Zagreb) mumps vaccine virus. Children who were the source of transmission had been vaccinated with the MMR vaccine (Serum Institute of India) contained L-Zagreb mumps virus. This is the first report of horizontal symptomatic transmission of this vaccine. The etiology of all seven contact cases was confirmed by epidemiological linking, serology and by F, SH, NP and HN mumps virus genes sequencing.