The objectives of these studies were to analyse the effect of mass influenza immunization in children on the morbidity of unvaccinated non-institutionalized elderly during an influenza epidemic. A mass vaccination campaign with vaccine was conducted in children aged 3-6 years attending kindergartens (57.4% of 6374) and aged 7-17 years attending schools (72% of 34237) in two communities of the Moscow region. The clinical effectiveness of vaccination was 60.9% for kindergartens and 68.8% for schools. There were 3.4 times fewer episodes of influenza-like illnesses and 1.7-2.6 fewer episodes in all seven diseases which are possible complications of influenza out of the 10 evaluated diseases in 158451 unvaccinated non-institutionalized elderly people during the influenza epidemic compared with the control communities. The differences were found to be statistically significant. Mass vaccination of children attending child institutions brought about a significant reduction of both influenza-like illnesses in children and influenza-associated illnesses in unvaccinated non-institutionalized elderly persons living in the home setting.