Efficacy and safety of COVID-19 vaccines: a systematic review

To evaluate systematically the efficacy and safety of COVID-19 vaccines.

PubMed, Embase, Cochrane Library, Clinicaltrial.gov, CNKI, Wanfang Data, China Biomedical Literature Service System, and China Clinical Trial Registry were searched for randomized controlled trials of COVID-19 vaccines published up to December 31, 2020. The Cochrane bias risk assessment tool was used to assess the quality of studies. A qualitative analysis was performed on the results of clinical trials.

Thirteen randomized, blinded, controlled trials, which involved the safety and efficacy of 11 COVID-19 vaccines, were included. In 10 studies, the 28-day seroconversion rate of subjects exceeded 80%. In two 10 000-scale clinical trials, the vaccines were effective in 95% and 70.4% of the subjects, respectively. The seroconversion rate was lower than 60% in only one study. In six studies, the proportion of subjects who had an adverse reaction within 28 days after vaccination was lower than 30%. This proportion was 30%-50% in two studies and > 50% in the other two studies. Most of the adverse reactions were mild to moderate and resolved within 24 hours after vaccination. The most common local adverse reaction was pain or tenderness at the injection site, and the most common systemic adverse reaction was fatigue, fever, or bodily pain. The immune response and incidence of adverse reactions to the vaccines were positively correlated with the dose given to the subjects. The immune response to the vaccines was worse in the elderly than in the younger population. In 6 studies that compared single-dose and double-dose vaccination, 4 studies showed that double-dose vaccination produced a stronger immune response than single-dose vaccination.

Most of the COVID-19 vaccines appear to be effective and safe. Double-dose vaccination is recommended. However, more research is needed to investigate the long-term efficacy and safety of the vaccines and the influence of dose, age, and production process on the protective efficacy.