WASHINGTON • Johnson & Johnson's (J&J) one-shot Covid-19 vaccine appeared safe and effective in trials, US Food and Drug Administration (FDA) staff said in documents published yesterday, paving the way for approval for emergency use.

The FDA's panel of independent experts meets tomorrow to decide whether to approve the shot.

While it is not bound to follow the advice of its experts, the FDA usually does and has authorised vaccines from Pfizer and Moderna.

J&J said in documents submitted to the FDA that its data suggested its vaccine was effective at preventing asymptomatic infections.

It added that in a preliminary analysis of its trial, it found 16 cases of asymptomatic cases in the placebo group versus two in the vaccine group, or an 88 per cent efficacy rate.

While asymptomatic infection was not the primary goal of the trial, which studied the vaccine's ability to stop moderate to severe Covid-19, the reduction of asymptomatic cases implies that the shot can also cut transmission of the disease.

J&J's vaccine was 66 per cent effective in preventing Covid-19 against multiple variants in a global trial involving nearly 44,000 people, the company said last month.

Its effectiveness varied from 72 per cent in the United States to 66 per cent in Latin America and to 57 per cent in South Africa, where a new variant has spread.

The vaccine was 85 per cent effective overall in stopping severe cases of the disease.

The shot was effective in reducing the risk of Covid-19 and preventing polymerase chain reaction-test confirmed infection at least 14 days after vaccination, the FDA said in its briefing documents.

Fourteen days after injection, only two vaccine recipients developed Covid-19 severe enough to need medical intervention, compared with 14 in the placebo group.

After 28 days, no vaccine recipients had complications severe enough to require medical treatment, whereas seven in the placebo group did.

Three vaccine recipients had severe side effects in the trial that were likely related to the shot.

But the FDA said its analysis did not raise any specific safety concerns that would preclude issuance of an emergency use authorisation.

The FDA said the most common solicited adverse reactions were injection site pain at 48.6 per cent, headache at 39 per cent, fatigue at 38.2 per cent and myalgia (muscle pain) at 33.2 per cent.

Other side effects included a fever in 9 per cent of the participants, while 0.2 per cent had a high fever.

REUTERS