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  • The FDA and CDC resumed the rollout of the Johnson & Johnson COVID-19 vaccine, with a warning about rare blood clots.
  • The CDC identified 15 cases of a rare blood clotting condition called thrombosis with thrombocytopenia syndrome (TTS) in people who had received the J&J vaccine.
  • Millions of people have received the vaccine with no major side effects.

All data and statistics are based on publicly available data at the time of publication. Some information may be out of date.

U.S. federal health officials said on April 23 that the Johnson & Johnson COVID-19 vaccine could restart, with vaccine fact sheets updated to warn of rare blood clot risks.

Several states moved quickly to resume their rollout of the one-dose vaccine.

The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) acted shortly after the CDC’s independent vaccine advisory committee recommended lifting the pause.

“Together, both agencies have full confidence that this vaccine’s known and potential benefits outweigh its known and potential risks in individuals 18 years of age and older,” acting FDA commissioner Dr. Janet Woodcock said in a media briefing on April 23.

On April 23, the CDC’s Advisory Committee on Immunization Practices (ACIP) looked at the risks and benefits of the J&J vaccine.

The CDC identified 15 cases of a rare blood clotting condition called thrombosis with thrombocytopenia syndrome (TTS) in people who had received the J&J vaccine.

As of April 21, three of these people had died, seven were still hospitalized, and five had been sent home.

This is out of nearly 8 million vaccine doses administered in the United States before the CDC and FDA recommended a pause in the use of the vaccine on April 13.

“Based on an in-depth analysis, there is likely an association, but the risk is very low. What we are seeing is the overall rate of events was 1.9 cases per million people,” CDC Director Dr. Rochelle Walensky said during the April 23 media briefing.

“In women 18 to 49 years, there was an approximate 7 cases per million. And the risk is even lower in women over the age of 50, at 0.9 cases per million,” she added.

Additional cases are under review, including among men.

The ACIP also looked at the benefits of resuming the J&J vaccine.

“For every 1 million doses of this vaccine, the J&J vaccine could prevent over 650 hospitalizations and 12 deaths among women aged 18 to 49, and this vaccine could prevent over 4,700 hospitalizations and nearly 600 deaths among women over 50,” Walensky said.

“These are significant numbers and show the important impact of this vaccine in our country,” she added.

During its meeting, the ACIP considered various scenarios, including restricting the use of the vaccine to people ages 50 years or older.

In the end, the committee voted to recommend use of the vaccine for people 18 years or older — the same as it had been before.

The FDA also updated the vaccine fact sheets for medical professionals and for vaccine recipients and caregivers to include information about the risk of rare blood clots accompanied by low platelet counts.

The final vote was 10 in favor of lifting the pause, 4 opposed, with 1 abstention.

“One of the reasons I think [the ACIP] decided to not have an age restriction on the vaccine is because the impact on COVID-19 deaths and ICU admissions is far greater if you make the vaccine widely available,” said Dr. Annabelle de St. Maurice, assistant professor of pediatrics in the Division of Infectious Diseases and co-chief infection prevention officer at UCLA Health, who was not a member of the committee.

Walensky said the pause in using the J&J vaccine allowed the CDC to identify any additional cases of these rare blood clots and inform healthcare professionals about the best way to treat this condition.

TTS is caused by an unusual immune reaction that targets platelets, which are cell fragments involved in clotting. This causes the platelets to clump together to form clots and results in a low platelet count.

Symptoms of TTS include severe headache, abdominal pain, leg pain, or shortness of breath. These show up about 1 to 2 weeks after vaccination.

“People who develop these symptoms should call their doctor sooner rather than later to get evaluated,” said de St. Maurice. “If they don’t have a regular doctor, then they should go to an emergency room or an urgent care center to get evaluated.”

Treatment for TTS includes using blood thinners — but not heparin, which can worsen the condition — and an immune product called IVIG to regulate the antibody response.

The ACIP discussed the possibility of providing an extra warning to women under the age of 50, who appear to have the highest risk of rare blood clots associated with the J&J vaccine.

However, this was not included in the committee’s final recommendation.

Dr. Robert Murphy, executive director of the Institute for Global Health and a professor of infectious diseases at Northwestern University, thinks there should be a stronger warning for younger women so they can adequately weigh the risks and benefits of the vaccine.

He added that he would steer his younger patients away from this vaccine whenever possible.

”I don’t see why any woman under 50 would want to take this vaccine,” he said, “unless there’s some burning reason why they can’t take an mRNA vaccine.”

The Moderna-NIAID and Pfizer-BioNTech COVID-19 vaccines have not been linked with this rare blood condition, the ACIP panel heard on April 23.

Murphy thinks the J&J vaccine should still be used, especially since its one-dose regimen and refrigerator storage make it more convenient for some people and locations.

This makes it an option for people who don’t want to return for a second dose, or for vaccinating people who can’t make it to a clinic or pharmacy.

“[This vaccine] is good for a lot of people who only want one shot,” Murphy said, “particularly people who are homebound or just can’t get that second shot or don’t want it.”

Already, a growing number of Americans are not completing their mRNA vaccination, leaving them with less than full protection. Recent CDC data shows that about 8 percent of Americans have missed their second dose — up from about 3.4 percent in March.

Making the vaccine available to all adults, with a clear warning about the blood clot risks, lets people make their own choice — based on their risk of blood clots and their risk of COVID-19.

“If you have risk factors for clotting — things like obesity, hypertension, hypothyroidism, or if you’re on oral contraceptives — you can make a personal decision about whether or not you should receive the Johnson & Johnson vaccine or one of the mRNA vaccines,” de St. Maurice said.

People with a higher risk of COVID-19 — such as those living in communities with high spread of the virus or working in frontline occupations — may also be more comfortable with a low risk of rare blood clots.

“That individual should weigh the risks and benefits of receiving a one dose vaccine, where you develop immunity just two weeks after that first dose,” de St. Maurice said, “versus getting a two-dose vaccine, where you need to wait at least four weeks before getting that second dose and then an additional two weeks after that to have the full effect.”