Comparing COVID-19 vaccines for their characteristics, efficacy and effectiveness against SARS-CoV-2 and variants of concern: A narrative review.

Background Vaccines are critical cost-effective tools to control the COVID-19 pandemic. However, the emergence of SARS-CoV-2 variants may threaten the global impact of mass vaccination campaigns. Objectives The objective of this study was to provide an up-to-date comparative analysis of the characteristics, adverse events, efficacy, effectiveness and impact of the variants of concern for nineteen COVID-19 vaccines. Sources References for this review were identified through searches of PubMed, Google Scholar, BioRxiv, MedRxiv, regulatory drug agencies and pharmaceutical companies' websites up to September 22nd, 2021. Content Overall, all COVID-19 vaccines had a high efficacy against the original strain and the variants of concern, and were well tolerated. BNT162b2, mRNA-1273 and Sputnik V had the highest efficacy (>90%) after two doses at preventing symptomatic cases in phase III trials. mRNA vaccines, AZD1222, CoronaVac were effective at preventing symptomatic COVID-19 and severe infections against Alpha, Beta, Gamma or Delta. Regarding observational real-life data, full immunization with mRNA vaccines and AZD1222 seems to effectively prevent SARS-CoV-2 infection against the original strain, Alpha and Beta but with reduced effectiveness against the Delta strain. A decline in infection protection was observed at 6 months for BNT162b2 and AZD1222. Serious adverse event rates were rare for mRNA vaccines (anaphylaxis: 2.5-4.7 cases per million doses), myocarditis (3.5 cases per million doses) and were similarly rare for all other vaccines. Prices for the different vaccines varied from $2.15 to $29.75 per dose. Implications All vaccines appeared to be safe and effective tools to prevent severe COVID-19, hospitalization, and death against all variants of concern, but the quality of evidence greatly varied depending on the vaccines considered. There are remaining questions regarding booster dose and waning immunity, the duration of immunity and heterologous vaccination. COVID-19 vaccine benefits outweigh risks, despite rare serious adverse effect.