Are Vaccines Effective and Safe for the Prevention of COVID-19 Infections? A Living Systematic Review

Abstract

Introduction. In the attempt to control the spread of the disease and the pandemic, numerous COVID-19 vaccines are in development. A review of the evidence on their efficacy and safety are critical. Methods. A search for trials was done using the COVID-19 Living OVerview of Evidence (L·OVE) platform. We also searched for relevant authorization documents and trial reports for COVID-19 vaccines of the US-Food and Drug Authority (US-FDA), the European Medicines Agency (EMA), the United Kingdom Medicines and Health Products Regulatory Agency (MHRA), and the WHO website. We included studies that fulfilled the following inclusion criteria: population – humans; intervention – COVID-19 vaccines; comparison – control or placebo; outcomes – efficacy and adverse events; methods – phase 3 randomized trials. Two reviewers independently screened the reports, assessed the methodological quality, and extracted the data on the trial characteristics and results on vaccine efficacy and safety. The date of last search was March 11, 2021. Results. Interim results of trials investigating five vaccines were identified and included in the review. All five vaccines demonstrated satisfactory vaccine efficacy (VE) against symptomatic COVID-19 infection among adults in the short term with moderate certainty of evidence: BNT162b2, VE 95% (95% CI 90.3, 97.6); mRNA-1273, VE 93.6% (95% CI 88.6, 96.5); ChAdOx1, VE 66.7% (95% CI 57.4, 74.0), Gam-COVID-Vac, VE 91.1% (95% CI 83.6, 95.1); and Ad26.CoV2.S, VE 67.2% (95% CI 59.3, 73.7). Data on the efficacy against severe COVID-19 infection and asymptomatic COVID-19 infection are still inconclusive, except for Ad26.CoV2.S, which demonstrated good efficacy in preventing moderate and/or severe COVID-19 infection and acceptable protection against asymptomatic COVID-19 infection 28 days after vaccination (moderate certainty of evidence). Efficacy data on preventing death from COVID-19 infection are still inconclusive. Very limited phase 3 trial data is available to inform vaccine efficacy against the different variants of SARS-CoV-2. Vaccination with these five vaccines was associated with higher adverse reactions compared to control. These adverse events, due to reactions to the vaccines, were mild to moderate and of short duration. Available evidence on vaccine efficacy and safety is limited, mainly due to the short follow up and the small sample size of specific populations. Conclusion. BNT162b2, mRNA-1273, ChAdOx1, Gam-COVID-Vac and Ad26.CoV.S vaccines demonstrated satisfactory vaccine efficacy against symptomatic COVID-19 infection among adults in the short term with moderate certainty of evidence. Data on the efficacy against severe COVID-19 infection, asymptomatic COVID-19 infection, and death from COVID-19 infection are still inconclusive. Long-term efficacy and safety data, and data on the efficacy against variant strains of SARS-CoV-2 are still lacking.