Researchers from the National Institute of Allergy and Infectious Diseases (NIAID), which is part of the National Institutes of Health (NIH), have found that two doses of an experimental COVID-19 vaccine rapidly controlled the coronavirus infection in the upper and lower airways of rhesus monkeys.

They also found that the vaccine candidate, called mRNA-1273, induced robust immune response to SARS-CoV-2, the virus that causes COVID-19.

The experimental vaccine is co-developed by Moderna Therapeutics and the NIAID Vaccine Research Center.

The animal study results were published online in the New England Journal of Medicine. Recently, Moderna released the findings of the Phase 1 clinical trial of the mRNA-1273 vaccine, which showed promising results in preventing COVID-19. The vaccine will be undergoing the Phase 3 trial, the last stage of the trial before approval.

In the animal study, three groups of eight rhesus monkeys received two doses of 10 or 100 micrograms (μg) of mRNA-1273 or a placebo. The second dose of the experimental vaccine was given 28 days after the first dose.

The study researchers found that vaccinated monkeys produced higher levels of neutralizing antibodies at the surface spike protein used by the virus to adhere to and enter cells.

The vaccine candidate also induced a specific immune response called Th1 T-cell response but not Th2 response. Also, the researchers found that the experimental vaccine helped induce T follicular helper T-cell responses that are associated with the robust antibody response.

After four weeks of the second dose, all the monkeys were exposed to the virus through the nose and the lungs.

Surprisingly, after two days of viral exposure, no replicating virus was detected in the lungs in seven out of eight of the monkeys in both vaccinated groups. However, the monkeys who received a placebo had viral replication in the lungs.

Furthermore, none of the eight vaccinated monkeys had detectable virus in their noses after two days of viral exposure.

This is probably the first time a COVID-19 vaccine candidate tested in animals produced such a rapid viral control in the upper and lower airways.

The researchers said, “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.” Globally, the virus has sickened more than 16 million people and killed over 663,000 so far. The United States officials have reported more than 4 million confirmed cases, with over 152,000 deaths.