What to Know About the Johnson & Johnson Vaccine Pause

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In a blow to national vaccination efforts, the FDA and CDC on Tuesday recommended a “pause” in the use of Johnson & Johnson’s single-shot COVID-19 vaccine because at least six people had developed severe blood clots after receiving it. The link between the two is not yet known. Below is what we know about the pause, the blood-clot issue, and what it means.

A temporary pause over a very rare condition

Dr. Janet Woodcock, acting FDA chief, says the agency expects the pause to last for only a matter of days. Agencies will convene a meeting on Wednesday to review cases and assess their potential significance given nearly 7 million Americans have received the shot with no major issue. The affected recipients were all between the ages of 18 and 48, with the clots showing up 6 to 13 days after immunization. One woman died, and one is in critical condition.

There is not yet a clear explanation for the clots. What makes this type of clot – called cerebral venous sinus thrombosis – unusual was that it was seen in combination with low levels of blood platelets. Though all six cases have appeared in women, the sample is too small to determine whether certain groups of people were at greater risk. (Oral contraception can also elevate the risk for blood clotting, but Marks says though all women who developed the side effect were of reproductive age, “it’s not clear that there’s any association with oral contraceptive pill birth control.”)

In part, the pause is in place so health-care providers can identify the rare clot and plan for the unique treatment required with this type of clot, Dr. Peter Marks of the FDA said in a press briefing on Tuesday. If one administers the standard treatment to these blood clots, “one can cause tremendous harm or the outcome can be fatal,” Marks says. “We have to take the time to understand this complication and address it properly.”

As a result of the recommended pause, federal sites will stop using the J&J vaccine, while states can decide on their own way forward. Already, multiple states across the country declared they would stop offering the shots for now. As of Tuesday, CVS and Walgreens will not be inoculating patients with the vaccine. The other two FDA-authorized vaccines, from Moderna and Pfizer, make up the vast share of COVID-19 shots already administered in the U.S. and are not affected by the pause.

Indeed, the shot’s pause will not have a significant impact on the nation’s vaccination plan, says Jeff Zients, White House COVID-19 coordinator: “We are working now with our state and federal partners to get anyone scheduled for a J&J vaccine quickly rescheduled for a Pfizer or Moderna vaccine.”

On Tuesday, Johnson & Johnson announced it will “proactively delay” the rollout of its vaccine in Europe which was due to start on Wednesday amid concerns about potential blood clots in American recipients.

How concerned should you be if you’ve already received the J&J vaccine?

“I know people who already got the vaccine are concerned,” Anne Schuchat, principal deputy director of the CDC, said in a press briefing on Tuesday. “If you got it over a month ago, the risk is really low. For people that just got the vaccine, they should be aware of any symptoms.”

In their joint statement, the CDC and FDA said people who have received the Johnson & Johnson vaccine who develop certain symptoms within three weeks of receiving the vaccine should contact their health-care provider. The symptoms were listed as severe headache, abdominal pain, leg pain, or shortness of breath.

Johnson & Johnson, in its own statement released Tuesday, said, “At present, no clear causal relationship has been established between these rare events and the Janssen COVID-19 vaccine. We continue to work closely with experts and regulators to assess the data and support the open communication of this information to health-care professionals and the public.”

“It’s a very rare event,” Dr. Carlos del Rio, executive associate dean of the Emory University School of Medicine, told CNN. “You’re talking about one per million, and when you give millions of doses of vaccines, you will see events like this that you couldn’t see in the clinical trial just because you didn’t have millions of people enrolled.” He thinks halting the vaccine’s rollout “is the right move until we understand what’s going on and what’s the way forward.”

“For most consumers, I wouldn’t be concerned about this,” says Dr. Scott Gottlieb, the FDA’s former commissioner told CNBC. “Really this is an alert to doctors. That’s how FDA framed it. It’s advice to doctors to be monitoring more closely.”

Why some have been eager to get the J&J shot

The Johnson & Johnson single-dose vaccine received emergency-use authorization from the FDA in late February with great fanfare, with hopes that its one-and-done nature and its relatively simple storage requirements would speed vaccinations across the country.

Yet the shot only makes up a small fraction of the doses administered in the U.S. as the pharmaceutical company has been plagued by production delays. Even before the news, the company’s vaccine was becoming increasingly difficult to obtain, after a mix-up at a factory in Baltimore meant it had to discard 15 million doses, slowing nationwide distribution.

Clotting concerns mirror issue with AstraZeneca vaccine

The call for a pause somewhat mirrors the situation that played out with the AstraZeneca vaccine last month, which isn’t in use in the United States, but has been authorized in more than 70 countries. Some European governments paused the vaccine’s rollout after a similarly tiny number of people suffered blood clots. Last week, the European Union’s drug regulator said the benefits of the vaccine outweigh its risks. Del Rio says that blood clotting may be connected to the vector-based technology both shots use: “The adenovirus vector vaccine may have something to do with it.”

The other two vaccines authorized for use in the U.S., from Pfizer and Moderna, use mRNA technology.

What to Know About the Johnson & Johnson Vaccine Pause