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One week after the FDA granted an emergency use authorization (EUA) for the Pfizer-BioNTech COVID-19 mRNA vaccine (BNT162b2; NEJM JW Infect Dis Dec 15 2020; [e-pub] and N Engl J Med 2020; 383:2603), the administration conferred an EUA for the Moderna COVID-19 mRNA vaccine (mRNA-1273) in a regimen of two 100-µg intramuscular doses 28 days apart (developed in collaboration with the National Institute of Allergy and Infectious Diseases Vaccine Research Center). Now, researchers report outcomes of the phase 3, placebo-controlled safety and efficacy study underlying this decision.
Between late July and late October of 2020, over 30,000 participants aged ≥18 years were enrolled. Through late November of 2020, results showed that the Moderna vaccine's efficacy against symptomatic COVID-19 occurring at least 14 days after the second dose was 94% (and a secondary analysis indicated that, 14 days after the first dose, efficacy was 95%). Efficacy was consistent in analyses stratified by age, sex, ethnic group, and risk factors for severe COVID-19; moreover, the vaccine was effective at preventing severe disease. Side effects mirrored those noted in the Pfizer-BioNTech mRNA vaccine trial (mild-to-moderate local reactions, fever, fatigue, headache, chills, muscle or joint pain, and nausea or vomiting; all more common after the second dose).
Baden LR et al. Efficacy and safety of the mRNA-1273 SARS-CoV-2 vaccine. N Engl J Med 2020 Dec 30; [e-pub]. (https://doi.org/10.1056/NEJMoa2035389)
Comment
Taken together, both mRNA COVID-19 vaccine trials provide reassurance that — at least for the observation period since July of 2020 — the mRNA platform seems to provide exceptional efficacy with only mild-to-moderate, generally acceptable side effects. In addition, no evidence has been found suggesting a risk for vaccine-associated enhanced disease (a problem that was seen with experimental vaccines developed for other respiratory viruses). Remaining questions concern long-term safety, durability of the immune response, efficacy against asymptomatic infection, prevention of viral shedding, and, perhaps most importantly, efficacy against infection with emerging SARS-CoV-2 variants.