In Russia, a universal varicella vaccination (UVV) program has not been implemented, and varicella vaccination coverage is low. We assessed the efficacy, antibody persistence, and safety of one- and two-dose varicella vaccination schedules in Russian children with a ten-year follow-up period, as part of an international phase IIIB, observer-blind, randomized, controlled trial (NCT00226499). Children aged 12-22 months were randomized (3:3:1) to receive two doses of tetravalent measles-mumps-rubella-varicella vaccine (V2 group), one dose trivalent measles-mumps-rubella (MMR) vaccine and one dose of varicella vaccine (V1 group), or two doses of MMR vaccine (V0 [control] group), 42 days apart. Main study outcomes were: vaccine efficacy (VE) against confirmed varicella cases, anti-varicella zoster virus (VZV) seropositivity rates and geometric mean concentrations, and reporting of (serious) adverse events ([S]AEs). The total vaccinated cohort in Russia comprised 1000 children; 900 were followed up until study end (year [Y] 10). VE estimates against confirmed varicella (Y10) were 92.4% in the V2 group and 74.7% in the V1 group. Anti-VZV seropositivity rates remained ≥99.4% in the V2 group and ≥89.7% in the V1 group from day 42 post-vaccination 2 until Y10. Occurrence of (un)solicited AEs and SAEs was similar across groups and confirmed the safety profile of the vaccines. No vaccination-related SAEs or deaths were reported. These results are consistent with the global trial results, i.e., the highest VE estimates observed following the two-dose schedule compared to the one-dose schedule. These data may inform decision-making related to potential implementation of a UVV program.
Keywords: Antibody persistence; Russia; children; combined vaccination; long-term efficacy; varicella.
What is the context?Varicella is a common childhood disease caused by the highly contagious varicella zoster virus.Varicella vaccines have been used for more than three decades.A large clinical trial conducted in ten countries assessed the efficacy and safety of one dose of monovalent varicella vaccine or two doses of combined varicella vaccine (MMRV). The enrolled children were also followed up for a ten-year period to evaluate the persistence of the immune response and the long-term efficacy of the vaccine.What is new?Here, we present the long-term efficacy, immunogenicity, and safety results in the cohort of children enrolled in Russia, as part of the global ten-year follow-up study. We found that:The monovalent and combined vaccines reduced the number of varicella cases.The MMRV two-dose regimen displayed higher efficacy in preventing varicella of all severities compared to the one-dose regimen.The immune response conferred by the vaccine persisted up to ten years post-vaccination.No vaccination-related deaths occurred, and no safety concerns were raised.What is the impact?Vaccination against varicella resulted in long-term protective efficacy and antibody persistence over ten years post-vaccination in Russian children.Although one-dose varicella vaccination was effective at protecting against varicella, a two-dose schedule provided a more complete protection. This could inform health policy decisions regarding the implementation of varicella vaccination in routine immunization program in Russia.