U.S. health agencies on Tuesday recommended pausing use of Johnson & Johnson's coronavirus vaccine while they investigate an apparent side effect to the shot.
In a joint statement, the Food and Drug Administration and the Centers for Disease Control and Prevention said they are reviewing cases of "rare and severe types of blood clots" in six women aged 18 to 48 who've been vaccinated with J&J's shot, as of April 12.
Peter Marks, the head of FDA division that reviews vaccines, said in a press conference Tuesday that one of the women died. A second is in critical condition.
The FDA and CDC emphasized that the events appear to be extremely uncommon, as nearly 7 million people in the U.S. have received J&J's vaccine. But they've called for vaccinations to be halted out of an abundance of caution during their investigation. The CDC will convene a public meeting of its expert vaccine advisory committee on Wednesday.
"We have been working closely with medical experts and health authorities, and we strongly support the open communication of this information to healthcare professionals and the public," J&J said in a statement.
The drugmaker said it plans to "proactively delay" the rollout of its vaccine in Europe, which was set to begin in the coming weeks.
The cases in the U.S. appear similar to the rare blood clotting that's been linked to AstraZeneca's vaccine in Europe, which has disrupted rollout of the shot in many countries there. J&J's vaccine, while different, uses a similar type of technology. Drug regulators in Europe have already begun investigating some of the cases that have occurred in the U.S.
The clotting associated with both vaccines to date are unusual and serious, occurring in veins that drain blood from the brain and alongside low levels of platelets, the sticky cells that help blood coagulate. The two reactions coinciding is particularly notable, and sparked concern among regulators.
Researchers in Germany, Norway and Austria have hypothesized the condition, at least as it relates to AstraZeneca's vaccine, resembles an autoimmune condition that can sometimes occur in people treated with the blood thinner heparin.
FDA and CDC officials didn't explicitly link the side effects to the two vaccines together, but noted the strong similarities on a conference call Tuesday. "I hesitate to call it a class effect but it is plainly obvious to us already that what we're seeing with [J&J's] vaccine looks very similar to what was seen with [AstraZeneca's] vaccine," Marks said on the conference call.
In their statement, the FDA and CDC indicated using heparin to treat the abnormal clots "may be dangerous," and recommended use of alternative anticoagulants.
The pause, they added, would help ensure healthcare providers are "aware of the potential for these adverse events" and can plan for the "unique treatment" that might be required for this type of blood clot.
"I think it was the prudent thing to do," said Paul Offit, director of the vaccine education center at Children's Hospital of Philadelphia and a member of the FDA's vaccine review committee, in an email to BioPharma Dive. "The association appears to be rare but real."
The agencies said people who have received J&J's vaccine and within three weeks experience severe headaches, leg or stomach pain, or shortness of breath should contact their healthcare provider.
"Right now, these adverse events appear to be extremely rare," they said. "COVID-19 vaccine safety is a top priority for the federal government, and we take all reports of health problems following COVID-19 vaccination very seriously."
Clinical testing of J&J's vaccine was temporarily halted in October when one trial participant who received the shot developed a rare, abnormal type of clot. But investigators couldn't find a link between the event and vaccination, and the pause — a typical precautionary step in large vaccine trial — was quickly lifted. No other, similar events were afterwards reported in the trial, and J&J's shot was found to be safe and strongly protective against COVID-19.
Still, health authorities in Europe and the U.S. now face a difficult communication challenge in appropriately warning of potentially serious side effects, while balancing that caution against the risk of COVID-19. In the U.S., supplies of vaccines from Pfizer and Moderna, which use a different technology, have increased dramatically and are likely sufficient to cover most adults.
White House COVID-19 response coordinator Jeff Zients said that, given the quickened pace of Pfizer and Moderna's manufacturing, there is currently "more than enough supply" for the U.S. to continue its current pace of vaccinating more than 3 million people per day. The U.S. government is working with states to ensure anyone set to receive a J&J shot will be quickly rescheduled for a Pfizer or Moderna vaccine. New York state, for instance, said that people scheduled for J&J's vaccine will now receive Pfizer's.
"This announcement will not have a significant impact on our vaccination plan," Zients said. J&J's shot makes up less than 5% of the total coronavirus vaccine doses administered in the U.S. so far.
But despite the large stockpile, news of J&J's rollout being paused could increase vaccine hesitancy at a time when cases have begun ticking higher. A slower vaccination pace — and more circulating infections — could give rise to additional variants, which could "put us in a perpetual cycle of catch-up with boosters," wrote RBC Capital Markets analyst Brian Abrahams.
FDA and CDC officials stressed Tuesday that the other two vaccines available in the U.S. haven't been linked to rare clotting events. Moderna, in a separate statement, said a safety review of the more than 64.5 million vaccinations administered globally "does not suggest an association" with such side effects.
"There are three vaccines available and we are not seeing these clotting events with low platelet counts with the other two vaccines," said Anne Schuchat, the principal deputy director of the CDC, in Tuesday's briefing.
In Europe, however, vaccinations have proceeded more slowly amid ongoing supply shortages. Many countries there were counting on AstraZeneca's vaccine to be the main shot for their immunization efforts, making the safety concerns a potentially costly setback in their efforts to protect their citizens against the virus.
Last week, the European Medicines Agency confirmed a possible link between AstraZeneca's vaccine and the rare clotting cases that have happened in some 200 people out of the 34 million who have received the shot in Europe and the U.K.
The EMA stressed the benefits of vaccination still outweigh the risks, noting the grave health threat still posed by COVID-19. Even so, government heath advisers in the U.K. have recommended other vaccines be used in place of AstraZeneca's for healthy adults under 30. France and Germany have advised younger people who received their first shot get to their second dose with a different vaccine.
Jonathan Gardner contributed reporting.