Effectiveness of monovalent vaccines in preventing death and severe disease among Omicron-infected and hospitalized patients in China.

BACKGROUND

The lifting of the zero-COVID policy in China in December of 2022 triggered a national surge of Omicron variants BA.5/BF.7 of SARS-CoV-2. The effectiveness of monovalent inactivated vaccines received by the majority of the Chinese population in reducing mortality and severe clinical outcomes among hospitalized patients with laboratory-confirmed BA.5/BF.7 infections remains unclear.

METHODS

In this retrospective cohort study, we extracted electronic health record (EHR) data on baseline characteristics, vaccination history, and clinical outcome of in-patients in three Chinese hospitals whose infections with SARS-CoV-2 were laboratory-confirmed and admitted during 25 November 2022 - 27 January 2023. Logistic regression was used to estimate vaccine effectiveness (VE) against death and severe disease (mechanical ventilator, intensive care unit or death), adjusting for potential confounders such as age group and chronic conditions.

RESULTS

Among the 862 patients with vaccination information, 360 (41.8 %) received at least one dose of COVID vaccine and only 214 (24.8 %) received ≥ 3 doses. The VE of ≥ 3 doses was estimated to be 74 % (95 % CI: 43 %, 88 %) against death and 65 % (95 % CI: 45 %, 78 %) against severe disease, in reference to unvaccinated. The two most widely used vaccines in China, Sinopharm and Sinovac, showed comparable effectiveness against death for ≥ 3 doses, 80 % (95 % CI: 9 %, 96 %) vs. 66 % (95 % CI: 18 %, 86 %), respectively.

CONCLUSIONS

While being replaced by more effective bivalent vaccines, monovalent inactivated vaccines can be a valuable option for preventing death and severe disease in resource-limited settings.