Animals receiving the 10-g or 100-g dose vaccine candidate produced neutralising antibodies in the blood
US biotechnology company Moderna's experimental vaccine to prevent Covid-19 induced robust immune responses and rapidly controlled the novel coronavirus in the upper and lower airways of monkeys exposed to SARS-CoV-2, according to a study.
The candidate vaccine, mRNA-1273, has been co-developed by scientists at Moderna and the National Institute of Allergy and Infectious Diseases (NIAID) in the US.
The study, published in the New England Journal of Medicine, complements recently reported interim results from an NIAID-sponsored Phase 1 clinical trial of mRNA-1273.
In the study, three groups of eight rhesus macaques received two injections of 10 or 100 microgrammes (g) of mRNA-1273 or a placebo. Injections were spaced 28 days apart.
Vaccinated macaques produced high levels of neutralising antibodies directed at the surface spike protein used by SARS-CoV-2 to attach to and enter cells, the researchers said.
Animals receiving the 10-g or 100-g dose vaccine candidate produced neutralising antibodies in the blood at levels well above those found in people who recovered from Covid-19, they said.
The researchers said the experimental vaccine also induced Th1 T-cell responses but not Th2 responses.
Induction of Th2 responses has been associated with a phenomenon called vaccine-associated enhancement of respiratory disease (VAERD), they said.
According to the researchers, vaccine-induced Th1 responses have not been associated with VAERD or other respiratory diseases.
The experimental vaccine also induced T follicular helper T-cell responses that may have contributed to the robust antibody response, they said.
Four weeks after the second injection, all the macaques were exposed to SARS-CoV-2 via both the nose and the lungs, according to the study.
It found that 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 replicating virus in the lung.
None of the eight macaques vaccinated with 100 g of mRNA-1273 had detectable virus in their noses two days after virus exposure, the researchers said.
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, the researchers noted.
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 transmission of SARS-CoV-2 and consequently reduce the spread of disease, they added.