because the Johnson & Johnson shot carries the risk of a rare but potentially fatal side effect that causes blood clots and bleeding in the brain.
In an emergency meeting on December 16, the CDC’s Advisory Committee on Immunization Practices, or ACIP, voted unanimously (15-0) to state a preference for the mRNA vaccines over the Johnson & Johnson shot. The vote came after the panel heard a safety update on cases of thrombosis with thrombocytopenia syndrome, or TTS, a condition that causes large clots that deplete the blood of platelets, resulting in uncontrolled bleeding.
The move brings the United States in line with other wealthy countries. In May, Denmark dropped the Johnson & Johnson shot from its vaccination program because of this risk. Australia and Greece have limited the use of a similar vaccine, made by AstraZeneca, in younger people because of the TTS risk. Both vaccines use the envelope of a different kind of virus, called an adenovirus, to sneak the vaccine instructions into cells. On Dec. 16, health officials said they had determined that TTS was likely due to a class effect, meaning it happens with all adenovirus vector vaccines.
The risk of dying from TTS after a Johnson & Johnson shot is extremely rare. There is an estimated 1 death for every 2 million doses of the vaccine given in the general population. That risk is higher for women ages 30 to 49, rising to about 2 deaths for every 1 million doses given in this age group. There’s no question that the Johnson & Johnson shot has saved many more lives than it has taken, experts said
Still, the committee previously paused the use of the Johnson & Johnson vaccine in April after the first cases of TTS came to light. That pause was lifted just 10 days later, after a new warning was added to the vaccine’s label to raise awareness of the risk.
In updating the safety information on Johnson & Johnson, the panel noted that the warning label had not sufficiently lowered the risk of death from TTS. Doctors seem to be aware of the condition because none of the patients who had developed TTS had been treated with the blood thinner heparin, which can make the syndrome worse. But patients continued to die even after the label was added, the panel noted, because TTS can progress so quickly that doctors simply don’t have time to treat it.
For that reason, and because there are other, safer vaccines available, the panel decided to make what’s called a preferential statement, saying the Pfizer and Moderna mRNA vaccines should be preferred over Johnson & Johnson.
The statement leaves the J&J vaccine on the market and available to patients who are at risk of a severe allergic reaction to the mRNA vaccines. It also means that people can still choose the J&J vaccine if they still want it after being informed about the risks.
About 17 million first doses and 900,000 second doses of the Johnson & Johnson vaccine have been given in the United States. Through the end of August, 54 cases of thrombosis with thrombocytopenia syndrome (TTS) have occurred after the J&J shots in the United States. Nearly half of those were in women ages 30 to 49. There have been nine deaths from TTS after Johnson & Johnson shots.
A version of this article first appeared on WebMD.com.