Impact of the emergence of severe acute respiratory syndrome coronavirus 2 omicron variants on routine childhood immunization in Japan

Abstract

BackgroundThe coronavirus disease 2019 (COVID-19) pandemic disrupted routine childhood vaccination worldwide, especially at the beginning of the pandemic. After the emergence of variants of concern, particularly the Omicron variants, the number of COVID-19 cases significantly increased, especially in children. However, the impact of the Omicron variants on routine childhood vaccination is unknown. MethodsThis retrospective observational study collected data on vaccines included in the Japanese national immunization program (NIP) of children 15 years or younger between 2016 and 2022 in Niigata, Japan. During the study period, hepatitis B virus vaccine and rotavirus vaccines were introduced to the NIP in October 2016 and October 2020, respectively. The monthly number of vaccine doses per eligible child population between 2020 and 2022 (pandemic period) was compared to the average number of vaccine doses in the corresponding month between 2016 and 2019 (pre-pandemic period). The effect of 8 surges of COVID-19 patients on trends in routine childhood vaccination was also analyzed. ResultsThe numbers of doses during the pre-Omicron pandemic period were comparable to the values administered before the pandemic. However, after the emergence of the Omicron variants, and especially after the surge of Omicron variant BA.5 in 2022, the number of vaccine doses declined. The decline was notable in second doses of MR vaccine at age 5–6 years by − 9.6 % and diphtheria-tetanus vaccine at ages 11–12 years by − 14.1 %. ConclusionsRoutine childhood immunization was significantly affected by the emergence of the Omicron variants most likely due to the facts that more candidates and their guardians contracted COVID-19, or were required isolation for close contacts. The findings highlight the importance of continued monitoring to maintain high coverage of routine childhood immunizations for controlling vaccine preventable diseases. A follow-up study should investigate changes in the number of declined vaccine doses during Omicron variant predominance.