Immunology: Safety and efficacy of Moderna vaccine booster doses assessed

Booster doses of the Moderna mRNA-1273 and variant-modified vaccines administered to 80 people were found to be safe and well-tolerated and increased levels of neutralizing antibodies against SARS-CoV-2 and key variants of concern—including Beta, Gamma and Delta. These results from an interim analysis of an ongoing clinical trial are published in Nature Medicine.

The emergence of SARS-CoV-2 variants of concern (VOCs) and interest (VOIs) with less susceptibility to antibody neutralization has generated interest in booster doses and variant-specific vaccines. In this analysis of the safety and efficacy of a booster dose against SARS-CoV-2, a group of participants who had received two doses of the Moderna (mRNA-1273) vaccine received a single booster dose six months later. This consisted of either the original vaccine or a variant-modified dose, such as the multi-variant mRNA-1273.211 vaccine.

Darin Edwards and colleagues observed four booster groups (with 20 participants per group) that received combinations of modified or original vaccines. Immediately before the booster dose, levels of neutralizing antibodies against SARS-CoV-2 in the blood had decreased relative to measurements one month after the participants received their second dose. Levels of neutralizing antibodies against the Beta, Gamma and Delta VOCs were also either low or undetectable. The authors found that all three booster vaccines tested increased levels of neutralizing antibodies against SARS-CoV-2 compared with the measurements obtained one month after the initial course of vaccinations, with significant increases for mRNA-1273 and mRNA-1273.211. In addition, all three boosters increased levels of antibodies against the Beta, Gamma and Delta variants, among other VOCs and VOIs.

The authors acknowledge several limitations to this preliminary analysis, including the small sample size and that the results are based on treatment groups that were not randomized. Nevertheless, they conclude that the mRNA platform approach against SARS-CoV-2 VOCs in this trial seems to be effective in the development of booster vaccines.