Johnson & Johnson's one-shot COVID-19 vaccine appeared safe and effective in trials, US Food and Drug Administration (FDA) staff said in documents published on Wednesday, paving the way for its approval for emergency use.The FDA's panel of independent experts meets on Friday 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 authorized 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 said 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% 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 the shot can also cut transmission of the disease.J&J's vaccine was 66% 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% in the United States to 66% in Latin America and 57% in South Africa, where a new variant has spread, though the vaccine was 85% effective overall in stopping severe cases of the disease.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. 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 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 likely related to the vaccine, but the FDA said its analysis did not raise any specific safety concerns that would preclude issuance of an emergency use authorization.The FDA said the most common solicited adverse reactions were injection site pain at 48.6%, headache at 39%, fatigue at 38.2% and myalgia at 33.2%. Other side effects included a fever in 9% of participants and a high fever in 0.2% of those who received the vaccine.The regulator said one case of pericarditis, a heart disease, may have been caused by the vaccine. It said cases of a rare disorder, Guillain-Barre Syndrome, were unlikely to be related to the shot though data was insufficient to determine whether the vaccine had caused these side effects or not.J&J had not previously released details of its clinical trial data beyond efficacy rates.