In a new study, researchers found that two doses of an experimental vaccine to prevent COVID-19 induced robust immune responses and rapidly controlled the coronavirus in the upper and lower airways.
The research was conducted by scientists from the National Institute of Allergy and Infectious Diseases (NIAID) and elsewhere.
The candidate vaccine, mRNA-1273, was co-developed by scientists at the NIAID Vaccine Research Center and at Moderna, Inc., Cambridge, Massachusetts.
The study complement recently reported interim results from an NIAID-sponsored Phase 1 clinical trial of mRNA-1273. The candidate mRNA-1273 vaccine is manufactured by Moderna.
In this study, three groups of eight rhesus macaques received two injections of 10 or 100 micrograms (µg) of mRNA-1273 or a placebo.
Injections were spaced 28 days apart. Vaccinated macaques produced high levels of neutralizing antibodies directed at the surface spike protein used by SARS-CoV-2 to attach to and enter cells.
The team found animals receiving the 10-µg or 100-µg dose vaccine candidate produced neutralizing antibodies in the blood at levels well above those found in people who recovered from COVID-19.
The experimental vaccine also induced Th1 T-cell responses but not Th2 responses.
Induction of Th2 responses has been linked to a phenomenon called vaccine-associated enhancement of respiratory disease (VAERD).
Vaccine-induced Th1 responses have not been associated with VAERD for other respiratory diseases.
In addition, the experimental vaccine-induced T follicular helper T-cell responses that may have contributed to the robust antibody response.
Four weeks after the second injection, all the macaques were exposed to SARS-CoV-2 via both the nose and the lungs.
Remarkably, after two days, no replicating virus was detectable in the lungs of seven out of eight of the macaques in both vaccinated groups, while all eight placebo-injected animals continued to have to replicate virus in the lung.
Moreover, none of the eight macaques vaccinated with 100 µg of mRNA-1273 had detectable virus in their noses two days after virus exposure.
This is the first time an experimental COVID-19 vaccine tested in nonhuman primates has been shown to produce such rapid viral control in the upper airway.
A COVID-19 vaccine that reduces viral replication in the lungs would limit disease in the individual while reducing shedding in the upper airway would potentially lessen the transmission of SARS-CoV-2 and consequently reduce the spread of disease.
The study is published in the New England Journal of Medicine.
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