Evidence of the Efficacy and the Effectiveness of First Generation COVID-19 Vaccines in Clinical Trials and Real-world Studies

More than 300 COVID-19 vaccine candidates have been developed or are currently in development. COVID-19 vaccines on the World Health Organization’s Emergency Use Listing and other COVID-19 vaccine products conditionally approved by national regulatory authorities are already in large-scale use, thus preventing severe illness or death and inducing herd immunity at the population level in the SARS-CoV-2 pandemic. In this review, we systemically assess the efficacy and effectiveness of COVID-19 vaccines in clinical trials or real-world studies, in various populations, including healthy adults, children, older people, pregnant people, people with cancer, and people receiving long-term hemodialysis or solid organ transplantation. In addition, we review available evidence regarding the effectiveness of COVID-19 vaccine immunization strategies in people with a history of SARS-CoV-2 infection, and the enhanced effectiveness conferred by various booster immunizations. We also discuss knowledge gaps in the persistence and spectrum of vaccine protection of currently available COVID-19 vaccines.