US weighs next steps for J&J virus shot amid clot mystery

U.S. health officials are weighing next steps as they investigate a handful of unusual blood clots in people who received Johnson & Johnson’s COVID-19 vaccine — a one-dose shot that many countries were eagerly awaiting to help speed virus protection.

It’s not clear if the exceedingly rare reports — so far, six cases out of more than 7 million inoculations in the U.S. — really are linked to the J&J vaccine. But the government recommended a pause in J&J vaccinations on Tuesday, just a week after European regulators declared that such clots are a rare but possible risk with the AstraZeneca vaccine, a shot made in a similar way but not yet approved for use in the U.S.

Experts say COVID-19 overall poses a much bigger risk of death and hospitalization than the potential clot threat. The next phase comes Wednesday, when advisers to the Centers for Disease Control and Prevention will debate in a public meeting how to handle the J&J vaccine while authorities try to nail down exactly what’s happening.

“Right now, we believe these events to be extremely rare, but we are also not yet certain we have heard about all possible cases as this syndrome may not be easily recognized,” CDC Director Rochelle Walensky said ahead of that meeting.

The clot concerns could undermine public confidence in a vaccine many hoped would help some of the hardest-to-reach populations — in poor countries or in places like homeless shelters in the U.S.

“We know we are fighting a war against COVID-19,” said Dr. Peter Marks, the Food and Drug Administration’s vaccine chief. But when it comes to side effects, “we don’t, in the United States, have a lot of tolerance for friendly fire.”

Marks said his agency recommended the J&J timeout less because of the number of reported clots than to make sure doctors...