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Efficacy of mRNA-1273 SARS-CoV-2 Vaccine After Blinded Phase
Quick Takes
- This study provides the final analyses of efficacy and safety data from the blinded phase of the mRNA-1273 vaccine (Moderna) for prevention of COVID-19.
- Results of the final analysis are consistent with the interim analysis.
- Two doses of mRNA-1273 vaccine were 98% effective in preventing severe COVID-19, and 63% effective in preventing asymptomatic infection, with no major differences across age, sex, race, and other relevant subgroups.
Study Questions:
Is the mRNA-1273 vaccine (Moderna) efficacious in preventing coronavirus disease 2019 (COVID-19) in adults at high risk of COVID-19 at least 14 days after the second dose?
Methods:
This study reports the vaccine efficacy and safety results of the final analysis of the blinded phase of the COVE trial. COVE was a phase 3, observer-blinded, randomized, placebo-controlled trial. Adults (≥18 years) in medically stable condition were enrolled at 99 sites in the United States. The blinded phase of the trial concluded when participants were informed of their group assignments. The open-label phase of the trial is currently ongoing. Participants were randomly assigned in a 1:1 ratio to receive two doses of the mRNA-1273 vaccine (100 μg) 28 days apart or placebo. The primary endpoint was prevention of COVID-19 illness with onset at least 14 days after the second injection in participants who had not previously been infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Safety measures included solicited local and systemic adverse events with onset during the 7 days after each injection and unsolicited adverse events with onset during the 28 days after each injection. The data cutoff date was March 26, 2021.
Results:
The trial enrolled 30,415 participants; 15,209 were assigned to receive the mRNA-1273 vaccine, and 15,206 to receive placebo. More than 96% of participants received both injections, 2.3% had evidence of SARS-CoV-2 infection at baseline, and the median follow-up was 5.3 months in the blinded phase. Vaccine efficacy in preventing COVID-19 illness was 93.2% (95% confidence interval [CI], 91.0-94.8), with 55 confirmed cases in the mRNA-1273 group (9.6 per 1,000 person-years; 95% CI, 7.2-12.5) and 744 in the placebo group (136.6 per 1,000 person-years; 95% CI, 127.0-146.8). The efficacy in preventing severe disease was 98.2% (95% CI, 92.8-99.6), with two cases in the mRNA-1273 group and 106 in the placebo group, and the efficacy in preventing asymptomatic infection starting 14 days after the second injection was 63.0% (95% CI, 56.6-68.5), with 214 cases in the mRNA-1273 group and 498 in the placebo group. Vaccine efficacy was consistent across ethnic and racial groups, age groups, and participants with coexisting conditions. Overall, 0.6% of placebo recipients and 0.4% of vaccine recipients had adverse events that resulted in their not receiving the second dose, and <0.1% in both groups discontinued trial participation because of adverse events after either injection. No cases of myocarditis were reported.
Conclusions:
The mRNA-1273 vaccine is safe and efficacious at preventing COVID-19.
Perspective:
Moderna’s mRNA-1273 vaccine is a lipid nanoparticle–encapsulated mRNA expressing the prefusion-stabilized spike glycoprotein of SARS-CoV-2. This final report of the blinded phase of the trial of mRNA-1273 confirms findings of efficacy and safety from the interim analysis that led to the Emergency Use Authorization by the Food and Drug Administration (FDA) for the use of this vaccine. The efficacy of the mRNA-1273 vaccine did not wane up to 4 months after the second injection. Post-vaccine deployment studies have shown that these findings have translated into high effectiveness in the general population and against variants such as the B.1.351 (beta) and B.1.617.2 (delta) variants. With regard to safety, clinical trials are not powered to detect rare events such as myocarditis or anaphylactic reactions. Continued vigilance and robust safety surveillance are warranted to identify subpopulations at risk of these rare events. Overall, real-world data show that the risk-benefit ratio for the vaccine is strongly in favor of broad deployment of vaccines in the adult population. Whether that will be the case in the pediatric population, where the risk of severe COVID-19 is much lower, remains to be seen.
Clinical Topics: COVID-19 Hub, Prevention
Keywords: Anaphylaxis, Asymptomatic Infections, Coronavirus, COVID-19, COVID-19 Vaccines, Nanoparticles, Primary Prevention, Risk Assessment, RNA, Messenger, SARS-CoV-2, Spike Glycoprotein, Coronavirus, Vaccine Potency
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