Sharis Carr, a nurse at the Aaron E. Henry Community Health Service Center in Clarksdale, Miss., holds a box containing doses of the Johnson & Johnson COVID-19 vaccine Wednesday, April 7, 2021. The U.S. is recommending a “pause” in using the single-dose Johnson & Johnson COVID-19 vaccine to investigate reports of potentially dangerous blood clots. (AP Photo/Rogelio V. Solis)

Sharis Carr, a nurse at the Aaron E. Henry Community Health Service Center in Clarksdale, Miss., holds a box containing doses of the Johnson & Johnson COVID-19 vaccine Wednesday, April 7, 2021. The U.S. is recommending a “pause” in using the single-dose Johnson & Johnson COVID-19 vaccine to investigate reports of potentially dangerous blood clots. (AP Photo/Rogelio V. Solis)

EXPLAINER: What’s known about COVID vaccines and rare clots

These are not typical blood clots – they’re weird in two ways

A rare, rogue immune response is the main suspect as authorities investigate highly unusual blood clots following use of two similar COVID-19 vaccines from Johnson & Johnson and AstraZeneca.

The U.S. recommended that states pause giving the J&J vaccine on Tuesday while authorities examine six reports of the unusual clots, including a death, out of more than 6.8 million Americans given the one-dose vaccination so far.

But the small number of cases sparked concern because just last week, European authorities said similar clots were possibly linked to the AstraZeneca vaccine, which is not yet OK’d in the U.S. That led some countries to limit its use to certain age groups. Also Tuesday, J&J delayed its imminent European rollout.

These are not typical blood clots. They’re weird in two ways.

First, they’re occurring in unusual parts of the body, such as veins that drain blood from the brain. Second, those patients also have abnormally low levels of platelets — cells that help form clots — a condition normally linked to bleeding, not clotting.

Scientists in Norway and Germany first raised the possibility that some people are experiencing an abnormal immune system response to the AstraZeneca vaccine, forming antibodies that attack their own platelets. That’s the theory as the U.S. now investigates clots in J&J vaccine recipients, Dr. Peter Marks, the Food and Drug Administration’s vaccine chief, said Tuesday.

The first clue: A widely used blood thinner named heparin sometimes causes a very similar side effect. Very rarely, heparin recipients form antibodies that both attack and overstimulate platelets, said Dr. Geoffrey Barnes, a clot expert at the University of Michigan.

“It kind of can cause both sides of the bleeding-clotting spectrum,” Barnes said. Because heparin is used so often in hospitals, that reaction is something “that every hospital in America knows how to diagnose and treat.”

There also are incredibly rare reports of this weird clot-low platelet combination in people who never took heparin, such as after an infection. Those unexplainable cases haven’t gotten much attention, Barnes said, until the first clot reports popped up in some AstraZeneca vaccine recipients.

Health officials said one reason for the J&J pause was to make sure doctors know how to treat patients suspected of having these clots, which includes avoiding giving heparin.

The Centers for Disease Control and Prevention later Tuesday provided advice on how to spot and treat the unusual clots.

In two studies in the New England Journal of Medicine last week, research teams from Norway and Germany found platelet-attacking antibodies in the blood of some AstraZeneca vaccine recipients who had the strange clots. The antibodies were similar to those found with the heparin side effect even though the patients had never used that blood thinner.

It’s not yet clear if there’s a similar link to the J&J vaccine. But the J&J and AstraZeneca vaccines, as well as a Russian COVID-19 vaccine and one from China, are made with the same technology. They train the immune system to recognize the spike protein that coats the coronavirus. To do that, they use a cold virus, called an adenovirus, to carry the spike gene into the body.

FDA’s Marks wouldn’t say if the weird clots may be common to these so-called adenovirus-vector vaccines. In addition to the AstraZeneca data, J&J makes an Ebola vaccine the same way and he said authorities would examine “the totality of the evidence.”

The most widely used COVID-19 vaccines in the U.S. — from Pfizer and Moderna — are made with a completely different technology, and the FDA said there is no sign of a similar clot concern with those vaccines.

What about people worried because they received the J&J vaccination? Marks said it’s important not to confuse the rare clot risk with normal flu-like symptoms people often feel a day or two after a COVID-19 vaccination. He said concerning symptoms, such as severe headache or severe abdominal pain, would occur a week to three weeks after the J&J vaccine.

___

The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.

Lauran Neergaard, The Associated Press

Coronavirusvaccines

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

Stock photo.
Grand Forks drug trafficker to be sentenced in Castlegar

Ryan Plotnikoff pleaded guilty to trafficking meth, following his November 2020 arrest by Grand Forks RCMP

Stuart Ashley Jones, 56, was at Grand Forks provincial court for sentencing on May 5, 2021. Photo: Laurie Tritschler
Grand Forks man shot by police during peak freshet sentenced to house arrest

Stuart Ashley Jones was shot by a Grand Forks Mountie after ramming two police cruisers in May 2018

Accused drug trafficker to plead to federal, provincial charges in June

Matthew Straume said he’d missed his last court date because he was ill

Photo: Laurie Tritschler
Grand Forks sex crimes trial adjourned until summer

The trial was set to begin at the city courthouse Wednesday, May 5

Photo: Kathleen Saylors
Grand Forks city council votes down motion to support Penticton in paramountcy battle

Coun. Neil Krog insisted Penticton’s issue with Victoria is about city bylaws, not homelessness

Thursday, Feb. 4: RDKB Chief Engineer Darryl Funk hoists a banner commemorating last year’s championship season by the Bantam House Bruins. Photo: Laurie Tritschler
Bantam Bruins honoured at hair-raising banner ceremony at Grand Forks’ Jack Goddard Arena

Asst. coach Mike Tollis said he reluctantly gave in to the team’s victory wish that he cut his pony tale

Junior A team Coquitlam Express is offering all Tri-City residents who get vaccinated against COVID-19 a free ticket to one of their games. (Facebook/Coquitlam Express)
B.C. hockey team offering free tickets to hometown fans who get the COVID-19 vaccine

‘We know the only way to get fans back is people getting vaccinated,’ says general manager Tali Campbell of the Coquitlam Express

Jobs Minister Ravi Kahlon speaks in the B.C. legislature, describing work underway to make a small business and tourism aid package less restrictive, Dec. 10, 2020. (Hansard TV)
B.C.’s latest COVID-19 restrictions cost thousands of service jobs

Part-time workers set back again by spike in virus spread

Cannabis bought in British Columbia (Ashley Wadhwani/Black Press Media)
Is it time to start thinking about greener ways to package cannabis?

Packaging suppliers are still figuring eco-friendly and affordable packaging options that fit the mandates of Cannabis Regulations

A sign indicating face coverings are required by the establishment is pictured on the front door of a business in Vancouver, B.C., Friday, April 9, 2021. COVID-19 cases have been on a steady increase in the province of British Columbia over the past week. THE CANADIAN PRESS/Jonathan Hayward
A sign indicating face coverings are required by the establishment is pictured on the front door of a business in Vancouver, B.C., Friday, April 9, 2021. COVID-19 cases have been on a steady increase in the province of British Columbia over the past week. THE CANADIAN PRESS/Jonathan Hayward
Leaked report shows detailed B.C. COVID-19 data not being released to public

Documents obtained by the Vancouver Sun show cases broken down by neighbourhoods

Abbotsford school board trustee Phil Anderson has stepped down after sharing an offensive image on Facebook. (File photo)
Abbotsford trustee temporarily steps down after sharing post relating COVID masks to slavery

Phil Anderson to receive training to better understand provincial mask mandate after posting picture

B.C. announced the launch of an app May 7 that connects youth struggling with mental health and substance use with “life-saving” social services. (Screen grab)
5 years in the making: Mental health app for youth and children launches in B.C.

The province provided $1.6-million to fund a virtual care platform

Amazon has announced the creation of five new facilities in B.C., to employ about 2,000 people. (Amazon/Special to Black Press Media)
Amazon adds new facilities in Langley, Pitt Meadows, Delta, Vancouver

The Vancouver port centre will be the first Amazon centre to feature robotics in B.C.

Mahitha Mohan is working in Nelson as a community support worker at Community Connections Support Services. Photo: Bill Metcalfe
Immigration pilot targets hard-to-fill jobs in West Kootenay

Program helps newcomers get permanent residency status in rural areas

Most Read