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

Public opposition to a planned road was expressed on posters on the hiking trails above the Nelson cemetery. Photo: Bill Metcalfe
Logging company abandons road construction planned near Nelson hiking trails

RDCK, public, and transportation ministry opposed the road

A concept of the new Kaslo Bridge, which is expected to be complete by November. Illustration: Ministry of Transportation and Infrastructure
Kaslo Bridge to be replaced

Construction on the $6.19-million project begins this month

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

The provincial government is funding upgrades to campgrounds in the Slocan Valley. File photo
Slocan Valley campgrounds to receive upgrades

New Denver, Slocan and Silverton have been granted $300,000

COVID-19 cases in B.C. for the week of April 25 to May 1. Illustration: BC Centre for Disease Control
Nelson surpasses 100 COVID-19 cases in 2021

The West Kootenays meanwhile saw numbers drop at the end of April

Protesters attempt to stop clear-cutting of old-growth trees in Fairy Creek near Port Renfrew. (Will O’Connell photo)
VIDEO: Workers, activists clash at site of Vancouver Island logging operation

Forest license holders asking for independent investigation into incident

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

The Canadian Coast Guard icebreaker Louis S. St-Laurent sails past a iceberg in Lancaster Sound, Friday, July 11, 2008. The federal government is expected to end nearly two years of mystery today and reveal its plan to build a new, long overdue heavy icebreaker for the Canadian Coast Guard. THE CANADIAN PRESS/Jonathan Hayward
Vancouver, Quebec shipyards to each get new heavy icebreaker, cost remains a mystery

Vancouver’s Seaspan Shipyards and Quebec-based Chantier Davie will each build an icebreaker for the coast guard

Findings indicate a culture of racism, misogyny and bullying has gripped the game with 64 per cent of people involved saying players bully others outside of the rink. (Pixabay)
Misogyny, racism and bullying prevalent across Canadian youth hockey, survey finds

56% of youth hockey players and coaches say disrespect to women is a problem in Canada’s sport

People line up outside an immunization clinic to get their Oxford-AstraZeneca COVID-19 vaccine in Edmonton, Tuesday, April 20, 2021. THE CANADIAN PRESS/Jason Franson
Hospital investigating whether Alberta woman who died after AstraZeneca shot was turned away

Woman was taken off life support 12 days after getting vaccine

People line up for COVID-19 vaccination at a drop-in clinic at Cloverdale Recreation Centre on Wednesday, April 27, 2021. Public health officials have focused efforts on the Fraser Health region. (Aaron Hinks/Peace Arch News)
B.C.’s COVID-19 spread continues with 694 new cases Thursday

Two million vaccine doses reached, hospital cases down

Allayah Yoli Thomas had recently turned 12 years old when she died of a suspected drug overdose April 15. (Courtesy of Adriana Londono)
Suspected overdose death of Vancouver Island 12 year old speaks to lack of supports

Allayah Yoli Thomas was found dead by her friend the morning of April 15

More than 6,000 camping reservations in British Columbia were cancelled as a result of a provincial order limiting travel between health regions. (Unsplash)
1 in 4 camping reservations cancelled in B.C. amid COVID-19 travel restrictions

More than 6,500 BC Parks campsite reservations for between April 19 and May 25 have been revoked

B.C. average home price and sales level to 2023, showing steep drop in sales expected next year. (Central 1)
Forecast calls for B.C. home sales to ‘explode,’ then drop off

Average price to rise another 10% in 2021, credit unions say

Most Read