CDC Panel Backs mRNA COVID Vaccines Over J&J Due to Rare Clot Risk

Brenda Goodman, MA

December 16, 2021

 Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

A panel of vaccine experts that advises the Centers for Disease Control and Prevention (CDC) on the use of vaccines in the United States said the Pfizer and Moderna mRNA COVID-19 vaccines should be preferred over the use of the Johnson & Johnson (J&J) shot for all adults because the J&J shot carries the risk for a rare but potentially fatal adverse effect that causes blood clots and bleeding in the brain.

In an emergency meeting on Thursday, the CDC's Advisory Committee on Immunization Practices (ACIP) voted unanimously (15-0) to state a preference for the mRNA vaccines over those from J&J after hearing a safety update on cases of thrombosis with thrombocytopenia syndrome (TTS). This condition 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 J&J 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 Thursday, Isaac See, MD, who is on the CDC's Vaccine Safety Team, said the agency had determined that TTS was likely due to a class effect, meaning it happens with all adenovirus vector vaccines.  

The risk for dying of TTS after a J&J shot is extremely rare. There is approximately one death for every 2 million doses of this vaccine given in the general population. That risk is higher for women age 30 to 49 years, rising to about two deaths for every million doses given in women in this age group. There's no question that the J&J shot has saved many more lives than it has taken.

Still, the ACIP paused the use of the J&J 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 the J&J vaccine today, the panel noted that the warning label had not sufficiently mitigated the risk for death from TTS.  Physicians seem to be aware of the condition because none of 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.

Preferential Statement

For that reason, and because other, safer vaccines are available, the panel decided to make what's called a preferential statement, stating the Pfizer and Moderna mRNA vaccines should be preferred over the J&J vaccine.

The statement leaves the J&J vaccine on the market and available to patients who are at risk for 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 J&J vaccine have been given in the United States. Through the end of August, 54 cases of TTS have occurred in the United States after the J&J shots. Nearly half of those were in women age 30 to 49 years.  

There have been nine recorded deaths from TTS after J&J shots.

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