Two doses of a U.S. experimental COVID-19 vaccine induced robust immune responses and controlled SARS-CoV-2, the virus that causes COVID-19, in the upper and lower airways of rhesus macaques exposed to the virus, study results published Tuesday showed.

The candidate vaccine, mRNA-1273, was co-developed by researchers at the U.S. National Institute of Allergy and Infectious Diseases and U.S. biotechnology company Moderna.

In the study published in the New England Journal of Medicine, three groups of eight rhesus macaques received two injections of 10 or 100 micrograms 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, said the study.

Animals receiving the 10-microgram or 100-microgram dose vaccine candidate produced neutralizing antibodies in the blood at levels well above those found in people who recovered from COVID-19, it said.

Four weeks after the second injection, all the macaques were exposed to the virus via both the nose and the lungs. Two days later, 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 lungs, the study said.

None of the eight macaques vaccinated with 100 micrograms of mRNA-1273 had detectable virus in their noses two days after virus exposure, according to the study.

A COVID-19 vaccine that reduces viral replication in the lungs would limit the disease in the individual, and reducing shedding in the upper airway would potentially lessen the transmission of the virus, the researchers said.