Johnson and Johnson vaccine appears to be 'safe and effective'

Documents released by the FDA said the watchdog's independent panel of experts had concluded that the firm's vaccine appeared to be "safe and effective" in trials.

The findings were a necessary key step before the vaccine was granted emergency use approval.

Clinical trials had shown the vaccine to be 88% effective in preventing asymptomatic infections.

That meant that 16 cases of asymptomatic infection were detected among the so-called 'control' group participating in trial who had not received the vaccine, but only two cases were found among those who had received it.

Significantly, that result implied that the vaccine was also able to reduce transmission of the virus between people who had been exposed to the virus and those who had not been.

All told, the vaccine's effectiveness against new strains of the virus around the world was put at roughly 66%, or 72% in the US, 66% in Latin America and 57% in South Africa.

Overall, the vaccine was 85% effective in preventing severe illness.

Fourteen days from receiving the vaccine, only two volunteers developed Covid-19 serious enough to warrant medical intervention, versus 14 in the placebo group.

After 28 days, none of those vaccinated required medical interventions, against seven from the control group.

Of the 40,000 volunteers enrolled in a late-stage trial, three reported severe side effects which likely were related to the J&J shot.

One case of pericarditis, a heart disease, might have resulted from the vaccine.