Immune Memory Response After a Booster Injection of mRNA-1273 for Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2)

Chu, L.; Montefiori, D.; Huang, W.; Nestorova, B.; Chang, Y.; Carfi, A.; Edwards, D. K.; Oestreicher, J.; Legault, H.; Girard, B.; Pajon, R.; Miller, J. M.; Das, R.; Leav, B.; McPhee, R.

Rising breakthrough infections of coronavirus-2 (SARS-CoV-2) in previously immunized individuals has raised concerns for a potential booster to combat suspected waning immunity and new variants. In this study, participants immunized 6-8 months earlier with a primary series of two doses of 50 or 100 g of mRNA-1273 were administered a booster injection of 50 g of mRNA-1273. Neutralizing antibody levels at one month after the booster were 1.7-fold higher than those one-month post primary series second injection meeting the prespecified criteria for noninferiority, and indicating an immune memory response. The reactogenicity after the booster dose was similar to that after the second dose in the primary series of two doses of mRNA-1273 (50 or 100 g) with no serious adverse events reported in the one-month follow-up period. These results demonstrate that a booster injection of mRNA-1273 in previously immunized individuals stimulated an immune response greater than the primary vaccination series.