Effectiveness of COVID-19 Vaccines and Post-vaccination SARS-COV 2 Infection, Hospitalization, and Mortality: a Systematic Review and Meta-analysis of Observational Studies

Abstract Introduction & ObjectiveVaccination is one of the most important and effective ways of preventing infectious diseases, and has recently been used in the COVID-19 epidemic and pandemic. The present meta-analysis study aimed to evaluate the effectiveness of COVID-19 vaccines in reducing the incidence of infection, hospitalization, and mortality in observational studies. Materials and MethodsA systematic search was performed independently in Scopus, PubMed, ProQuest, and Google Scholar electronic databases as well as Preprint servers using the keywords under study. The heterogeneity of the studies was assessed using I2and χ2 statistics, according to which the I2 of > 50% and P -value <0.1 was reported as heterogeneity of the studies. In addition, the Pooled Vaccine Effectiveness (PVE) obtained from the studies was calculated by converting (1-Pooled estimate × 100%) based on the type of outcome. ResultsA total of 54 records were included in this meta-analysis. The rate of PVE against SARS-COV 2 infection was about 71% (OR = 0.29, 95% CI: 0.23-0.36) in the first dose and 87% (OR = 0.13, 95% CI: 0.08-0.21) in the second, and the highest effectiveness in the first and second doses was that of BNT162b2 mRNA and combined studies. The PVE versus COVID-19-associated hospitalization was 73% (OR = 0.27, 95% CI: 0.18-0.41) in the first dose and 89% (OR = 0.11, 95% CI: 0.07-0.17) in the second. mRNA-1273 and combined studies in the first dose and ChAdOx1 and mRNA-1273 in the second dose had the highest effectiveness. Regarding the COVID-19-related mortality, PVE was about 28% (HR = 0.39, 95% CI: 0.23-0.45) in the first dose and 89% (HR = 0.11, 95% CI: 0.03-0.43) in the second. ConclusionThe evidence obtained from this study showed that the effectiveness of BNT162b2 mRNA, mRNA-1273, and ChAdOx1 in the first and second doses, and even combined studies were associated with increased effectiveness against SARS-COV2 infection, hospitalization, and death from COVID-19. In addition, considering that the second dose was significantly more efficient than the first one, a booster dose injection could be effective in high-risk individuals. On the other hand, it was important to observe other prevention considerations in the first days after taking the first dose.