Johnson & Johnson’s one-shot coronavirus vaccine is safe and effective, the US Food and Drug Administration said on Wednesday.
The assessment paves the way for the drug’s emergency use in the US, and experts will meet on Friday to decide whether to approve it.
While it is not bound to follow the advice of its experts, the FDA usually does, and authorised vaccines from Pfizer-BioNTech and Moderna.
J&J said in documents submitted to the FDA that its data suggested its vaccine was effective at preventing asymptomatic infections.
It said that in preliminary analysis of its trial, it found 16 cases of asymptomatic cases in the placebo group compared with two in the vaccine group, or 88 per cent efficacy.
While measuring 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 implied the shot could also cut transmission of the disease.
J&J’s vaccine was, on average, 66 per cent effective in preventing Covid-19 against variants in a global trial involving about 44,000 people, the company said last month.
Its effectiveness varied from 72 per cent in the US to 66 per cent in South America to 57 per cent in South Africa, where a new, highly contagious variant was first identified.
The vaccine was effective in reducing the risk of Covid-19 and preventing PCR test-confirmed Covid-19 at least 14 days after vaccination, the FDA said in its briefing documents.
A fortnight 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 developed Covid severe enough to require medical intervention, whereas seven in the placebo group did.
Three vaccine recipients had severe side effects in the trial that were probably related to the vaccine.
But the FDA said its analysis did not raise any specific safety concern that would prevent authorisation for emergency use.
The most common adverse reactions were injection site pain at 48.6 per cent, headache at 39 per cent, fatigue at 38.2 per cent and myalgia, or muscle pain, at 33.2 per cent.
Other side effects included a fever in 9 per cent of participants and a high fever in 0.2 per cent of those who received the vaccine.
The regulator said one case of pericarditis, a heart condition, might have been caused by the vaccine.
It said cases of a rare disorder in which the immune system attacks the nerves, Guillain-Barre syndrome, were unlikely to be related to the shot, although data was insufficient to determine whether or not the vaccine had caused it.
J&J had not previously released details of its clinical trial data beyond efficacy rates.