Rare cases of clotting that have been seen with two Covid-19 vaccines have put the spotlight on an uncommon reaction that occurs when the body unleashes its immune firepower against blood platelets.
Health officials are exploring whether and how the immune reaction may occur in people who have received vaccines made by AstraZeneca Plc and Johnson & Johnson. Concerns have risen so high that the U.S. Centers for Disease Control and Prevention and Food and Drug Administration jointly recommended a pause in the use of the J&J vaccine on Tuesday.
The syndrome is highly unusual in that it involves increased clotting along with low levels of platelets, the blood component mainly responsible for coagulation, and has only been seen at low rates in vaccine recipients. The pressure is on for governments that want to hasten immunizing millions of people over the next few months to understand the risk and avoid panic.
“The more challenging issue is how do we make a responsible, right communication to the public,” said Behnood Bikdeli, a cardiologist at Harvard Medical School and Brigham and Women’s Hospital who studies clotting and Covid. “We want to be transparent, but we want to make sure that we’re not scaring people out of proportion. In order of magnitude, the problem is Covid.”
Adenovirus Link
The appearance of severe, hard-to-predict blood clotting events in two leading vaccines is a setback in the race to vaccinate as many people as possible before next winter. It raises the possibility that some of the vaccines that were being counted on to deliver worldwide supply could have significant restrictions placed upon them that could limit their use, as is already happening with AstraZeneca’s vaccine in Europe.
The Astra and J&J vaccines both use an adenovirus to help the immune system identify and battle the coronavirus. Other similar vaccines, Russia’s Sputnik V shot and one from China’s CanSino Biologics Inc., may also come under scrutiny.
CanSino said it uses a different type of adenovirus vector than either Astra or J&J. There haven’t been reports of any serious cases of blood clotting among the 1 million poeple who have received the shot, the company said in a Hong Kong stock exchange filing.
Six women from ages 18 to 48 suffered a type of blood clot in the brain called cerebral venous sinus thrombosis after getting the J&J vaccine, health officials said Tuesday, with one woman dead and another in critical condition. The patients all had low levels of blood platelets, a suspicious similarity to a complication that has been observed with the vaccine from AstraZeneca and the University of Oxford.
It’s also similar to another rare clotting disorder that occurs in people treated with heparin. While the anticoagulant is normally used to prevent blood clots, in rare cases it will turn the immune system against a platelet protein, which leads to dangerous reduction of levels and substantial clotting.
Both the Astra and the J&J vaccines are “likely inducing anti-platelet antibodies,” leading to activation of the platelets and cerebral blood clots in rare cases, says Peter Jay Hotez, an immunization expert at the Baylor College of Medicine in Houston.
“Each county will need to make decisions about continuing” with using the vaccines, or deciding on restrictions on their use, he said. “This is a problem for Africa and Latin America” as those countries were heavily depending on adenovirus vaccines for their rollout.
Heparin Concern
People who have the vaccine reaction probably shouldn’t receive heparin, said Jeff Weitz, a professor at McMaster University and president of the International Society on Thrombosis and Hemostasis. Other options like Bristol-Myers Squibb Co.’s Eliquis or J&J’s Xarelto are probably safer oral medications, he said.
The pause on the J&J vaccine will give CDC and FDA time to review the situation and make sure doctors who see the clotting syndrome know how to respond, said Peter Marks, director of the FDA’s Center for Biologics Evaluation and Research. The events were seen between 6 and 13 days after vaccination, and were identified by FDA through a government-run vaccine adverse event reporting system, Marks said in a webinar sponsored by the American Medical Association.