Preliminary Study of the Protectiveness of Vaccination Against the COVID-19 in the Outbreak of VOC Omicron BA.2 - Jilin City, Jilin Province, China, March 3-April 12, 2022.

WHAT IS ALREADY KNOWN ABOUT THIS TOPIC?: An outbreak of coronavirus disease 2019 (COVID-19) of Omicron BA.2 emerged in Jilin City since March 3, 2022, which involved in 27,036 cases by April 12. The vaccination program with inactivated COVID-19 vaccines has been implemented since the beginning of 2021.

WHAT IS ADDED BY THIS REPORT?: The incidences of moderate, severe, and critical cases in the whole population of the group of 0+1 dose were 1.82-, 9.49-, and 3.85-fold higher than those in the group of 2 doses, and 5.03-, 44.47-, and ∞-fold higher than those received 3 doses vaccination. For the population ≥60 years, the incidences of moderate, severe, and critical cases in the group of 0+1 dose were 29.92, 9.62, and 4.27 per 100,000, showing 4.13-, 43.72-, and 4.85-fold higher than 2 doses, as well as 13.28-, 22.37-, and ∞-fold higher than 3 doses.

WHAT ARE THE IMPLICATIONS FOR PUBLIC HEALTH PRACTICE?: The incidences of each type of COVID-19 in the population who were fully vaccinated or booster vaccinated in Jilin City were significantly lower than those who were unvaccinated and/or partially vaccinated. Booster vaccination with homologous inactivated vaccines induces stronger protectiveness for COVID-19 caused by variant of concern (VOC) Omicron.