Vaccination with mRNA-1273, Moderna’s coronavirus disease 2019 (COVID-19) vaccine candidate, led to robust immune responses and protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in nonhuman primates, according to new data recently published in The New England Journal of Medicine.

The study evaluated a 2-dose vaccination schedule of 10mcg (n=8) or 100mcg (n=8) doses or placebo (n=8) given 4 weeks apart. Following the second dose, the animals were challenged with high doses of SARS-CoV-2 by intratracheal and intranasal routes.

Results showed that the vaccine induced antibody responses above those seen in human convalescent plasma, consistent with the findings observed in the phase 1 human trial. Neutralizing antibody titers further increased at the higher dose.

Additionally, vaccination was associated with a significant increase in T-cell responses. “These data show that mRNA-1273 induced [type 1 helper T-cell] and interleukin-21–producing [T follicular helper]-cell responses. We did not find evidence of [type 2 helper T-cell] or CD8 T-cell responses,” the study authors reported.

Two days after viral challenge, 7 of the 8 animals in each vaccine group demonstrated protection against viral replication in the lungs, while in the 100mcg group, none of the animals had detectable viral replication in the nose. Moreover, substantial inflammation was not observed in the lungs of animals vaccinated with the 100mcg dose at day 7 or 8 after challenge; inflammation was found to be mild in the 10mcg group at day 7.

The study authors also reported that no viral RNA was detected at day 7 in either group, however at day 8, a pneumocyte positive for viral antigen was detected in 1 animal in the 10mcg group.

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“We believe this is the first demonstration of control of viral replication within 2 days of challenge in both the nose and lungs in nonhuman primates by a vaccine against COVID-19,” said Stephen Hoge, MD, President at Moderna.  “Given the similarity between the protective immune response generated by mRNA-1273 in this study and the immune response seen in humans in the recently published phase 1 clinical data for the vaccine, we remain cautiously optimistic that mRNA-1273 will be able to prevent COVID-19 disease and may also slow the spread of SARS-CoV-2 by shortening the duration of shedding.” 

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  1. Corbett KS, Flynn B, Foulds KE, et al. Evaluation of the mRNA-1273 vaccine against SARS-CoV-2 in nonhuman primates [published online July 28, 2020]. The New England Journal of Medicine. doi: 10.1056/NEJMoa2024671.
  2. Moderna announces publication in The New England Journal of Medicine of non-human primate preclinical viral challenge study of its mRNA vaccine against COVID-19 (mRNA-1273). Published July 28, 2020. Accessed July 29, 2020.