Real-World Effectiveness of Primary Series and Booster Doses of Inactivated Coronavirus Disease 2019 Vaccine Against Omicron BA.2 Variant Infection in China: A Retrospective Cohort Study

Abstract

Background China has been using inactivated COVID-19 vaccines as primary series and booster doses to protect the population from severe to fatal COVID-19. We evaluated primary and booster vaccine effectiveness (VE) against Omicron BA.2 infection outcomes. Methods This was a 13-province retrospective cohort study of quarantined close contacts of BA.2-infected individuals. Outcomes were BA.2 infection, COVID-19 pneumonia or worse, and severe/critical COVID-19. Absolute VE was estimated by comparison with an unvaccinated group. Results There were 289,427 close-contacts ≥3 years old exposed to Omicron BA.2 cases; 31,831 turned nucleic-acid amplification test (NAAT)-positive during quarantine, 97.2% with mild or asymptomatic infection, 2.6% had COVID-19 pneumonia, and 0.15% had severe/critical COVID-19. None died. Adjusted VE against any infection was 17% for primary series and 22% when boosted. Primary series aVE in adults >18 years was 66% against pneumonia or worse infection and 91% against severe/critical COVID-19. Booster dose aVE was 74% against pneumonia or worse, and 93% against severe/critical COVID-19. Conclusions Inactivated COVID-19 vaccines provided modest protection from infection, very good protection against pneumonia, and excellent protection against severe/critical COVID-19. Booster doses are necessary to provide strongest protection.

Long-Term Immunogenicity and Safety of a Homologous Third Dose Booster Vaccination with TURKOVAC: Phase 2 Clinical Study Findings with 32-Week Post-Booster Follow-Up

“…The GMTs of IgGs, which remained above the lower limit of seroconversion throughout the study period, might be explained by the persistence of specific immune memory cells allowing for antibody production following exposure to the relevant antigens. Overall, our findings show the clinical efficacy of boosting with TURKOVAC in preventing SARS-CoV-2 infection and reducing COVID-19 severity and are complementary to those from previous studies of various inactivated vaccines which reported low rates of infection, pneumonia, hospitalization, and death associated with SARS-CoV-2 infection after the administration of a booster dose [ 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ].…”

Vaccines reduced hospital length of stay and fraction of inspired oxygen of COVID-19 patients: A retrospective cohort study

“…According to the World Health Organization (WHO) data, by December 2022, 50 vaccines have been approved by at least one country worldwide ( Chakraborty et al, 2023 ), which include whole virus live attenuated or inactivated, protein-based, viral vector, and nucleic acid vaccines ( Ndwandwe and Wiysonge, 2021b ). As of 1 December 2022, over 13 billion COVID-19 vaccine doses have been administered ( Tang et al, 2023 ). In China, as of 31 December 2022, China has reported more than 3.4 billion cumulative doses of the COVID-19 vaccines ( Ma et al, 2023 , Sun et al, 2023 ).…”

Inactivated SARS-CoV-2 Vaccine Booster Against Omicron Infection Among Quarantined Close Contacts

“…[25][26][27] For example, our estimate was much lower than that of an mRNA vaccine found in an RCT conducted during the Delta-predominant period (95.3%; 95% CI, 89.5%-98.3%), 28 but was closer to that of a recombinant protein vaccine (47.8%; 95% CI, 22.6%-64.7%) in another RCT 29 conducted during the Omicron-predominant period. Furthermore, previous general population studies 25,27,[30][31][32] reported that the effectiveness of a booster dose of an Model 1 (left) was adjusted for age, sex, health care practitioner, diabetes, hypertension, chronic kidney disease, stroke, cancer, interval between the first and second doses, and interval between the latest dose and last contact. Model 2 (right) was further adjusted for calendar time of last contact.…”