[Periodicity of chickenpox and epidemic parotitis].

The pattern of the dynamics of incidence of chickenpox and epidemic mumps in Leningrad for many years was studied. The application of mathematical methods of treatment of the incidence data revealed the main trends of the processes and the occurrence of three rhythms in each infection. The average values of the periods of these rhythms differ for chickenpox and epidemic mumps and are 11.0, 6.2, and 4.1 years and 8.2, 4.0, and 2.8 years, respectively. The study of the age incidence in comparison with the dynamics of the epidemic process for many years showed that periodicity of these infections could not be explained completely by variations of the herd immunity of the population.