Moderna's COVID-19 Vaccine Deemed 'Highly Effective,' but Further Studies Needed

Caleb Rans, PharmD

December 24, 2020

The Food and Drug Administration's Vaccines and Related Biological Products Advisory Committee (VRBPAC) evaluated Moderna's COVID-19 vaccine as highly effective with a favorable safety profile, based on interim data from an ongoing phase 3 trial.

The panel acknowledged that further studies will be required post issuance of an Emergency Use Authorization (EUA) to collect additional data on the safety and effectiveness of the vaccine. A briefing document released by the FDA on Dec. 17, 2020, summarized interim results and included recommendations from VRBPAC on use of Moderna's mRNA-1273 COVID-19 vaccine.

"On November 30, 2020, ModernaTX (the Sponsor) submitted an EUA request to FDA for an investigational COVID-19 vaccine (mRNA-1273) intended to prevent COVID-19," the committee wrote.

The mRNA-1273 Vaccine Trial

Among 30,351 individuals aged 18 years and older, the efficacy, safety, and immunogenicity of the mRNA-1273 vaccine candidate was evaluated in a randomized, stratified, observer-blind, placebo-controlled phase 3 study. Participants were randomly assigned (1:1) to receive two injections of either 100 mcg of mRNA-1273 (n = 15,181) or saline placebo (n = 15,170) administered intramuscularly on day 1 and day 29.

The primary efficacy endpoint was efficacy of mRNA-1273 against PCR-confirmed COVID-19 with onset at least 14 days following the second dose. The primary safety endpoint was to characterize the safety of the vaccine following one or two doses.


Among 27,817 subjects included in the first interim analysis (data cutoff: Nov. 7, 2020), 5 cases of COVID-19 with onset at least 14 days after the second dose occurred among vaccine recipients and 90 case occurred among placebo recipients, corresponding to 94.5% vaccine efficacy (95% confidence interval, 86.5%-97.8%).

"Subgroup analyses of the primary efficacy endpoint showed similar efficacy point estimates across age groups, genders, racial and ethnic groups, and participants with medical comorbidities associated with high risk of severe COVID-19," they reported.

Data from the final scheduled analysis of the primary efficacy endpoint (data cutoff: Nov. 21, 2020; median follow-up of >2 months after dose 2), demonstrated 94.1% vaccine efficacy (95% confidence interval, 89.3%-96.8%), corresponding to 11 cases of COVID-19 in the vaccine group and 185 cases in the placebo group.

When stratified by age, the vaccine efficacy was 95.6% (95% CI, 90.6%-97.9%) for individuals 18-64 years of age and 86.4% (95% CI, 61.4%-95.5%) for those 65 years of age or older.

In addition, results from secondary analyses indicated benefit for mRNA-1273 in preventing severe COVID-19 cases, COVID-19 in those with prior SARS-CoV-2 infection, and infection after the first dose, but these data were not conclusive.


Among 30,350 subjects included in the first interim analysis (data cutoff: Nov. 11, 2020; median follow-up of 7 weeks post second dose), no specific safety concerns were observed that would prevent issuance of an EUA.

Additional safety data (data cutoff: Nov. 25, 2020; median follow-up of 9 weeks post second dose) were provided on Dec. 7, 2020, but did not change the conclusions from the first interim analysis.

The most common vaccine-related adverse reactions were injection site pain (91.6%), fatigue (68.5%), headache (63.0%), muscle pain (59.6%), joint pain (44.8%), and chills (43.4%).

"The frequency of serious adverse events (SAEs) was low (1.0% in the mRNA-1273 arm and 1.0% in the placebo arm), without meaningful imbalances between study arms," they reported.

Myocardial infarction (0.03%), nephrolithiasis (0.02%), and cholecystitis (0.02%) were the most common SAEs that were numerically greater in the vaccine arm than the placebo arm; however, the small number of cases does not infer a casual relationship.

"The 2-dose vaccination regimen was highly effective in preventing PCR-confirmed COVID-19 occurring at least 14 days after receipt of the second dose," the committee wrote. "[However], it is critical to continue to gather data about the vaccine even after it is made available under EUA."

The associated phase 3 study was sponsored by ModernaTX.

SOURCE: FDA Briefing Document: Moderna COVID-19 Vaccine. FDA Vaccines and Related Biological Products Advisory Committee. Published Dec. 17, 2020.

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