Top U.S. health officials on Tuesday called for a pause in the use of the Johnson & Johnson COVID-19 vaccine while they review cases of rare blood clots in people receiving the shots.
The officials said they are reviewing six cases of a "rare and severe type of blood clot" out of more than 6.8 million people in the U.S. who have received the Johnson & Johnson vaccine.
All six cases were in women between ages 18 and 48.
The Centers for Disease Control and Prevention's (CDC) Advisory Committee on Immunization Practices will meet on Wednesday to review the cases, and the Food and Drug Administration (FDA) will look into them as well.
"Until that process is complete, we are recommending a pause in the use of this vaccine out of an abundance of caution," said Peter Marks, a top FDA official, and Anne Schuchat, a top CDC official, in a joint statement. "This is important, in part, to ensure that the health care provider community is aware of the potential for these adverse events and can plan for proper recognition and management due to the unique treatment required with this type of blood clot."
The type of blood clot in question, called cerebral venous sinus thrombosis, requires different treatment than blood clots usually do. The agencies said they want health providers to be able to plan for them.
Marks and Schuchat stressed that "these adverse events appear to be extremely rare."
"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," the officials added. "People who have received the J&J vaccine who develop severe headache, abdominal pain, leg pain, or shortness of breath within three weeks after vaccination should contact their health care provider."
The move is sure to send shockwaves through the U.S. vaccination effort and could worsen vaccine hesitancy, which was already a problem as some people refused to be inoculated.
Still, two other vaccines, from Pfizer and Moderna, have made up the bulk of U.S. supply so far, and no serious safety issues have been raised with them.
About 7 million Johnson & Johnson shots have been administered in the U.S. so far, compared to much higher numbers for Pfizer and Moderna, about 98 million and 85 million, respectively.
Health officials stressed during a call with reporters that the blood clots are "extremely rare," but said time is needed to alert health care providers on how to treat patients who do have the issue. The standard treatment for blood clots, a drug called heparin, could cause "tremendous harm," for patients who got the vaccine, so doctors need to know to use alternate treatments, Marks said.
"The time frame will depend obviously on what we learn in the next few days, however we expect it to be a matter of days for this pause," said acting FDA Commissioner Janet Woodcock.
Asked if the pause was an overreaction given how rare the blood clots appear to be, officials pointed to a balance with alerting health care providers and the severity of the pandemic.
"When we saw this pattern and were aware that treatment needed to be individualized for this condition, it was of the utmost importance for us to get the word out," Schuchat said. "That said, the pandemic is quite severe and cases are increasing in a lot of places and vaccination is critical, so we want to make sure that we make some recommendations quickly."
Officials said there have not been any reports of this blood clotting problem in people receiving the Pfizer and Moderna vaccines.
Johnson & Johnson had also been struggling with its manufacturing, with problems at a Baltimore plant delaying the distribution of more doses. But there are about 9 million more Johnson & Johnson shots that have been distributed, according to CDC data, that are now subject to a pause.
"While unfortunate, it's the right step," Ashish Jha, dean of the Brown School of Public Health, wrote of the pause on Twitter. "Central to vaccination success is ensuring people have confidence they are safe. These events (central venous thrombosis) are VERY rare. 6 out of 7 million. No vaccine (or drug) is perfect. But confidence is built on having a system that takes adverse events seriously, investigates them, makes data-driven decisions."
The move brings home to the U.S. some of the back-and-forth that has played out in Europe over a different vaccine, from AstraZeneca, that has been subject to a pause in some countries due to rare blood clots as well. That vaccine has not yet been approved by the FDA for use in the U.S.
Updated at 11 a.m.