Extremely rare but life-threatening blood clots linked to the Johnson & Johnson COVID-19 vaccine appear similar to those caused by the AstraZeneca vaccine approved for use in Europe and Canada, U.S. health officials said Tuesday.

Federal officials called for a “pause” in use of the one-dose J&J vaccine while they review data linked to six women between 18 and 48 years of age who developed blood clots a week to two weeks after their shots. The officials stressed that decisions on whether to get the shot should be left to individuals.

“This is a recommendation. It’s not a mandate,” Dr. Peter Marks, director of the U.S. Food and Drug Administration’s Center for Biologics Evaluation and Research, said during a media briefing. “If an individual health care provider has a conversation with an individual patient and they determine that the benefit/risk for that individual patient is appropriate, we’re not going to stop that provider from administering the vaccine.”

Of the six cases, one woman died, and another is in critical condition, Marks said.

The “pause” is largely intended to provide time to get the word out to clinicians about how to appropriately treat these vaccine-related blood clots, Marks said.

The gold-standard treatment for dangerous clots is a blood thinner called heparin, but that drug has been linked to the same sort of clotting syndrome occurring with the AstraZeneca and Johnson & Johnson vaccines.

“The issue here with these types of blood clots is that if one administers the standard treatment that we as doctors have learned to give for blood clots, one can actually cause tremendous harm or the outcome can become fatal,” Marks said.

Worries about vaccine hesitancy

Infectious disease experts are concerned that this pause will further heighten the public’s concern about COVID vaccine safety, and will harm vaccination efforts that are meant to head off a fourth wave of U.S. infections.

“This action will likely add to vaccine hesitancy and will do irreparable harm to the vaccine rollout and will bleed into the other vaccines as well. This risk-averse stance will likely cost lives and delay control of the pandemic,” said Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore.

More than 6.8 million doses of the J&J vaccine have been administered in the United States so far, with only six people developing dangerous clots, he said.

“This is less than one in a million, and certainly less than the risk of blood clots from getting COVID itself,” Adalja said. “The risk-benefit ratio strongly favors this vaccine, and I worry that these decisions are going to cause a litany of cancellations for the Johnson & Johnson vaccine and a relegating of it to the second tier when regulators ultimately say that the risk-benefit ratio strongly favors the vaccine and lift the federal pause.”

A White House coronavirus adviser said the pause “will not have a significant impact” on U.S. vaccination efforts, the Associated Press reported.

The J&J vaccine represents fewer than 5% of shots administered in the United States, according to Jeff Zients, the White House COVID-19 response coordinator.

“We are working now with our state and federal partners to get anyone scheduled for a J&J vaccine quickly rescheduled for a Pfizer or Moderna vaccine,” Zients said in a statement.

‘Careful deliberation’

A wave of states immediately announced that they would honor the pause, but Marks said Tuesday that people who want the J&J vaccine at this time can talk with their health care provider and go ahead with the shot.

The six cases involved what’s known as a cerebral venous sinus thrombosis (CVST), a rare type of clot seen in combination with low levels of blood platelets, according to a joint statement from the FDA and the U.S. Centers for Disease Control and Prevention.

The CDC’s Advisory Committee on Immunization Practices plans to meet Wednesday to further review the cases, Dr. Anne Schuchat said during the briefing. Schuchat is the CDC’s principal deputy director.

“This will allow careful deliberation about what we know so far about these events, and consider next steps given the current context of the COVID-19 pandemic in the United States,” she told reporters.

People should not be worried if they develop a headache right after they get vaccinated for COVID, as this is one of the common side effects caused by the immune system’s uptake of the vaccine, Marks said.

“For people who recently got the vaccine within the last couple of weeks, they should be aware to look for any symptoms,” Schuchat said.

Symptoms include severe headache, abdominal pain, leg pain or shortness of breath. Any of these could indicate formation of a blood clot, she said. You shouldn’t be worried if you got a J&J vaccine much earlier — for those who got the shot more than a month ago, the risk is very low, Schuchat said.

mRNA vaccines unaffected

The officials noted that this dangerous clotting has only been seen in the AstraZeneca and Johnson & Johnson vaccines, and not in the mRNA vaccines developed by Pfizer and Moderna.

“There have been over 180 million doses of those vaccines administered, and at this time we’ve not found any reports” of dangerous blood clots, Marks said of the mRNA vaccines. According to The New York Times, more than 23 million doses a week of those shots are now being distributed across the United States.

The AstraZeneca vaccine appears to cause some people to develop antibodies that target a protein in the body called platelet factor 4 (PF4). It spurs platelets into action and activates a clotting cascade, according to recent case reports in the New England Journal of Medicine.

The phenomenon is similar to a rare drug side effect caused by the blood thinner heparin, which is called heparin-induced thrombocytopenia, according to Dr. Theodore Warkentin, a professor of pathology and molecular medicine at McMaster University in Hamilton, Ontario, Canada. He co-authored one of the NEJM reports.

The vaccine’s clotting side effects are so rare that European and U.K. regulatory agencies both decided to keep it on the market, concluding that the benefits outweigh the risks, AstraZeneca noted in a statement.

There are established ways to treat heparin-induced thrombocytopenia, and those could provide a clue how to help patients with vaccine-linked blood clots, Warkentin said.

Doctors sometimes treat heparin-induced thrombocytopenia by administering high doses of IV immunoglobulin, essentially flooding the body with healthy antibodies to drown out the clotting signal produced by the drug, he explained.

“We’re recommending that when a doctor recognizes such a patient with this new condition called vaccine-induced immune thrombotic thrombocytopenia, they be treated not only with anticoagulation but with this high-dose intravenous immunoglobulin,” Warkentin said.

Other setbacks

In a statement, Johnson & Johnson said that “we are aware that thromboembolic events including those with thrombocytopenia have been reported with COVID-19 vaccines,” the Times reported, and “at present, no clear causal relationship has been established between these rare events and the Janssen COVID-19 vaccine.” Janssen is the Johnson & Johnson division that developed the vaccine.

The news came as another blow to vaccination efforts worldwide. In Europe, concerns have been raised over AstraZeneca’s vaccine after 222 similar cases of clotting occurred, out of 34 million shots administered in Britain and the European Union, the Times noted. The AstraZeneca vaccine is not being used in the United States.

The CDC/FDA pause marks another recent setback for J&J vaccine in the United States.

The federal government had already announced that Johnson & Johnson would allocate 86% fewer doses of its coronavirus vaccine across the country this week.

The slowdown came days after federal officials learned that Emergent BioSolutions, a contract manufacturer that has been making both the Johnson & Johnson and the AstraZeneca vaccines in a Baltimore plant, had mixed up ingredients from the two and ruined up to 15 million doses of the Johnson & Johnson vaccine. How big a role that problem has played in its distribution woes is hard to determine, the Times said.

The U.S. coronavirus case count passed 31.2 million Tuesday, while the death toll passed 562,000, according to a Times tally.

More information

The U.S. Centers for Disease Control and Prevention has more about COVID-19 vaccines.

SOURCES: Peter Marks, MD, PhD, director, Center for Biologics Evaluation and Research, U.S. Food & Drug Administration; Amesh Adalja, MD, senior scholar, Johns Hopkins Center for Health Security, Baltimore; Anne Schuchat, MD, principal deputy director, U.S. Centers for Disease Control and Prevention; Theodore Warkentin, MD, professor, pathology and molecular medicine, McMaster University, Hamilton, Ontario, Canada; Associated Press; New York Times

Source: HealthDay