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Safety and Immunogenicity of SARS-CoV-2 mRNA-1273 Vaccine in Older Adults

Our take —

The findings in this study of older adults, who are a high risk group for illness and death from COVID-19, were similar to those found in younger adults. Results were promising for use of the mRNA-1273 vaccine in this small group of older adults, and findings indicate that a second dose may be required in this age group in order to achieve high levels of neutralizing antibodies. The 100ug dose with a 2 dose strategy will be tested in a larger phase 3 study in a more diverse population.

Study design

Randomized Controlled Trial

Study population and setting

This study was an expansion of the phase 1 trial that tested the mRNA-1273 vaccine, a stabilized version of the mRNA for SARS-CoV-2 spike protein (S-2P) encapsulated in lipid nanoparticles, manufactured by Moderna. The trial took place between April 16 and May 12, 2020, adding a group of 20 participants between 56 and 70 years old, and 20 participants 71 years and older. The trial was conducted in Seattle, WA; Atlanta, GA; and Bethesda, MD. Subjects received two doses of vaccine in the deltoid administered 28 days apart, in two evenly divided dose groups of either 25ug or 100ug. The main objectives were to study safety and immunogenicity of the vaccine in this population of older adults and expand on the original data from 18 to 55 year old participants.

Summary of Main Findings

No serious adverse events were reported in the trial. Adverse events more commonly occurred after the second dose, with moderate severity, including fatigue, chills, headache, myalgia, and pain at the injection site. These mainly occurred the day of or day after vaccination and resolved quickly. Binding antibody responses to the S-2P protein increased after the first vaccine dose. In the 56-70 year old age group, antibody levels reached the upper quarter of the distribution among convalescent plasma donors after the second dose, and in the age 71+ years group the response was even more robust. Serum neutralizing antibodies were also detected in all participants following the second dose, and this was confirmed by multiple methods. Finally, S-specific T-cell responses were observed following the second vaccine dose.

Study Strengths

This study was one of the first to address safety and immunogenicity of a SARS-CoV-2 vaccine in those of older age, which is extremely important since they are one of the most vulnerable populations. Next, results from participants were compared to antibody levels in convalescent serum samples. Finally, neutralizing antibody responses were tested against the newer 614G strain in addition to the original 614D (Wuhan-1) strain, and it still showed a robust response. This is a reassuring confirmation that mRNA-1273 should still be effective against the newer strain.


This study only included 40 participants, and therefore statistical comparisons were not informative due to small group sizes. The small size may also limit detection of rare serious adverse events at long-term follow-ups. Almost all of the participants were white, and therefore this study should not be generalized to other racial groups which are being affected by the virus. Finally, long-term durability of the immune response was not assessed here, although it is planned.

Value added

Insight into safety and immunogencity of Moderna’s mRNA-1273 vaccine in a population of older adults, which is unique compared to other SARS-CoV-2 vaccine clinical trials.

This review was posted on: 9 October 2020