A long-term trend in the incidence of viral hepatitis A (VHA) in relation to vaccine prevention of this disease and poliomyelitis were analyzed in the Krasnodar Territory. There were lower VHA morbidity rates, which coincided with the period of additional mass immunization of children against poliomyelitis. Comparison of the frequency of polio vaccination and the trend in VHA incidence suggests that the viral interference phenomenon is involved in the regulation of its epidemic process, as a result of which vaccine poliomyelitis virus suppresses naturally circulating hepatitis virus A.