On Oct. 21, 2021, the National Institutes of Health announced that a booster dose of the mRNA-1273 COVID-19 vaccine given to rhesus macaques about six months after their primary vaccine series significantly increased levels of neutralizing antibodies against all known SARS-CoV-2 variants of concern.

The study, published in Science, also showed that the increased neutralizing antibody responses were sustained for at least eight weeks after the boost, were significantly higher than after the primary vaccine series, and generated high-level protection ﾖ meaning the ability to significantly limit virus from replicating in the lungs and nose.