Updated at 12 p.m. ET
Johnson & Johnson has paused all clinical trials of its experimental COVID-19 vaccine after a study participant became sick with an "unexplained illness."
In a statement on Monday, the company said it had "temporarily paused further dosing in all our COVID-19 vaccine candidate clinical trials," including a Phase 3 trial that began late last month, while it investigated the illness.
"Adverse events — illnesses, accidents, etc. — even those that are serious, are an expected part of any clinical study, especially large studies," the company said.
The Johnson & Johnson Phase 3 trial of its Janssen COVID-19 vaccine candidate involves an anticipated 60,000 adults in multiple countries, testing the safety and efficacy of a single dose versus a placebo. A two-dose regimen is being tested in a separate trial.
In a conference call on Tuesday morning to discuss the company's finances, Johnson & Johnson said it had learned about the participant's illness on Sunday evening and immediately informed an independent data and safety monitoring board.
Mathai Mammen, who leads global research and development at Janssen, Johnson & Johnson's pharmaceutical division, said on the call that the company does not yet know whether the participant had received the vaccine or a placebo.
The independent safety board has the right to unblind the study, Mammen said, but the company remains blinded for now.
"We know very little at this point, and it will be a few days at minimum for the right set of information to be gathered and evaluated," he said. Details about the nature of the illness were not provided.
Johnson & Johnson's pause isn't the first time a COVID-19 vaccine trial has been halted due to health safety concerns. Last month, the Phase 3 trial of a vaccine candidate from AstraZeneca was put on hold after a British study participant developed a neurological illness. The AstraZeneca study resumed a few days later in the United Kingdom and elsewhere, though it remains on hold in the U.S.
In a statement earlier this month, AstraZeneca said it "continues to work with the Food and Drug Administration (FDA) to facilitate review of the information needed to make a decision regarding resumption of the US trial" and the safety of trial participants is "paramount."
The Johnson & Johnson vaccine candidate was the fourth participant in the Trump administration's Operation Warp Speed program to move into Phase 3. It has the benefit of not needing to be frozen, and may require only one shot rather than two.
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