Objectives: We systematically reviewed the literature to investigate the pooled effect of COVID-19 mRNA vaccination against SARS-CoV-2 infection and its clinical outcomes.

Methods: Scopus, Web of Science, PubMed (Medline), and Embase were searched on 9 September 2021. The odds ratio (OR) of COVID-19 infection and its clinical outcomes in fully/ partially vaccinated versus unvaccinated participants were calculated and pooled by using a random-effects model.

Results: The pooled analysis showed that among health care workers and general population, vaccinated participants with one or two doses were less likely to infect with SARS-CoV-2 (OR = 0.16; 95%CI: 0.08-0.32; I² = 79.86%; 95%CI I²: 68.99-87.21%), to develop symptomatic COVID-19 infection (OR = 0.09; 95%CI: 0.03-0.32; I² = 80.43%; 95%CI I²: 70.83-89.33%), to admit to the hospital because of COVID-19 (OR = 0.13; 95%CI: 0.06-0.28; I² = 86.19%; 95%CI I²: 67.80-93.88%), and to die from COVID-19 (OR = 0.14; 95%CI: 0.06-0.35; I² = 66.76%; 95%CI I²: 54.00-76.99%) than unvaccinated participants.

Conclusions: COVID-19 mRNA vaccines, especially following administration of two doses, are extremely effective. It would be suggested further studies with large sample size and different ethnicities to be conducted among the general population to warrant these results.