Boosting nonhuman primates with Moderna vaccine increases neutralizing antibody responses

Boosting nonhuman primates with the Moderna vaccine (mRNA-1273) six months after their primary vaccine series increased neutralizing activity against viral variants of concern, a new study shows.

"It may be important to boost antibody responses, especially against [variants of concern], to sustain and increase protection against severe disease, particularly in at-risk cohorts, and to reduce the potential for mild infection and transmission" in the setting of waning immunity, the authors say.

Neutralizing antibody responses gradually wane against several variants of concern (VOC) after vaccination with the SARS-CoV-2 vaccines that deliver the spike protein, including the Moderna vaccine (mRNA-1273). Since mRNA-1273 was granted emergency use authorization in December 2020 and deployed globally, many months have elapsed since the first individuals were vaccinated, and the durability of vaccine protection remains a concern.

Additionally, the question of whether an additional booster vaccination is necessary particularly as new variants of concern become more prevalent is clinically relevant. Kizzmekia Corbett and colleagues evaluated the immune responses in nonhuman primates that received two doses of the mRNA-1273 vaccine (a primary vaccination series) and were boosted about six months later with either mRNA-1273 (homologous) or mRNA-1273.β (heterologous), which encompasses the spike sequence of the B.1.351 variant.

Following the boost, the animals exhibited increased neutralizing antibody responses across all variants, which suggests there is significant B cell memory induced by primary mRNA vaccination that can be rapidly recalled following the boost, the authors say. This response was sustained for at least eight weeks after the boost. Nine weeks after the boost, the animals were challenged with the SARS-CoV-2 B.1.351 variant. Their viral replication was low to undetectable in bronchoalveolar samples studied, and it was greatly reduced in nasal swabs.