US scientists are expanding a government-funded study that aims to directly answer the question of whether Moderna Inc's Covid-19 vaccine curbs the spread of Sars-CoV-2.

The study, backed by the National Institutes of Health (NIH), was originally was designed to be tested among college students — some of whom would get the vaccine on a delayed basis — but it will now be broadened to adults aged 18-29, including those who choose not to receive a vaccine, the Covid-19 Prevention Network, which is overseeing the US Covid-19 vaccine trials, said.

“If our study demonstrates that a Covid-19 vaccine works to prevent infection and transmission of the virus, many more people may decide to get vaccinated, which has huge public health implications,” said Dr Larry Corey, a vaccine expert at Fred Hutchinson Cancer Centre in Seattle, and principal investigator of the network's operations.