CNN reported on Thursday that early stage trials of US pharmaceutical company Johnson & Johnson's (J&J) experimental COVID-19 vaccine indicated it generated an immune response in nearly all volunteers, with minimal side-effects, after a single dose.

Reportedly, researchers who tested the vaccine in a combined Phase 1-2 trial, mostly meant to show safety, found either one or two doses of the vaccine generated both antibody and T-cell responses against COVID-19.

These trials were not designed to show whether the vaccine protected people against either infection or symptoms of COVID-19, as that is what the ongoing Phase 3 trials are designed to do.

An international team of researchers, who tested the COVID-19 vaccine in around 800 volunteers, wrote in the New England Journal of Medicine that the early stage trials showed the vaccine was safe and probably should work.

These researchers, based in the Netherlands, the US and Belgium, had tested the vaccine in a group of people 65 and older and a group ages 18 to 55.

In their report, the researchers said the vaccination elicited neutralising antibodies, expected to stop the virus from infecting cells, in 90% of all participants by the 29th day after the first dose of vaccine and in all of them by two months after the first dose. The levels of these antibodies stayed stable for at least 71 days.

J&J expects to report details of more advanced trials later in January 2021 and is hoping to apply for authorisation from the US Food and Drug Administration soon after.