CNN reported on Wednesday that a study done in monkeys suggests Moderna's experimental COVID-19 vaccine might protect against severe disease and reduce the risk of passing the virus along to others.

US biotechnology company Moderna started advanced, Phase 3 testing of its experimental vaccine in humans in the US on 27 July 2020, the fastest advancement ever of a new vaccine in the US. However, the quick vaccine development process means the vaccine was not tested extensively in animals before moving on to people.

A team at the National Institute of Allergy and Infectious Diseases (NAID), which helped develop the vaccine, tested it in rhesus macaque monkeys. Then they infected the monkeys with the virus, an experiment that would be difficult, ethically, to do in human.

While the monkeys did become infected, the vaccine appeared to interfere with the spread of the virus in the animals, the NIAID team reported in The New England Journal of Medicine.

None of the monkeys that got the higher dose of vaccine had virus in their noses, either. That would suggest the vaccine might prevent the spread of the virus, even if people do get infected.

"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 investigators note," the NAID 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 transmission of SARS-CoV-2 and consequently reduce the spread of disease," they added.

The researchers note that its not at all clear that monkeys respond to the virus in the same way that people do. But they noted that the virus appears to replicate in the noses of the monkeys in much the same way as it does in people.

Also, one worry was that the vaccine might make the body overreact to a true infection later on, a response known as vaccine-associated enhanced respiratory disease. This didn't happen in the monkeys, the researchers said.