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

From now to November, WildsafeBC will be educating the public through its various programs in the community of Bella Coola. (Black Press Media file photo)
Bears are back, and so is WildSafeBC

Rae will be working hard to reach out to community members in new and innovative ways

Bella Coola’s new WildSafeBC co-ordinator, Rae Kokeš, has spent the last 10 years in Africa working in lion, human, conflict, and is a wildlife biologist by trade. (Photo submitted)
From the savannas of Africa to the Bella Coola Valley

New Wildsafe BC coordinator ready to tackle wildlife conflict

RCMP crest. (Black Press Media files)
Stolen truck found broken down on Highway 97C, Williams Lake suspect arrested near Ashcroft

A security guard first noticed the truck, and thought it looked suspicious

This will be the second year the Bella Coola Valley Rodeo won’t take place due to the pandemic. (Michael Wigle file photo)
Bella Coola Valley Rodeo cancelled for 2021

Club organizers say next year’s rodeo will be bigger and better than ever

Cameron Lang, (left) poses with his brothers Casey Lang and Colton Lang and their father Scotty Lang while volunteering at 100 Mile’s first Heavy Metal Rocks program in 2019. (Photo submitted)
Heavy Metal Rocks prepares alumni for professional world

Casey Lang got a new perspective from the class

(The Canadian Press)
Trudeau won’t say whether Canada supports patent waiver for COVID-19 vaccines

‘Canada is at the table to help find a solution’

A map showing where the most number of cases were recorded from April 23 to 29. This map, revealing a breakdown of infections by neighborhood, was pulled from a data package leaked to the Vancouver Sun last week (and independently verified).
36 Abbotsford schools flagged for COVID-19 exposures in the last 2 weeks, shattering record

Clearbrook Elementary recorded an ‘exposure’ on all 11 school days

Canada’s chief public health officer is reminding Canadians even those who are fully vaccinated are not immune from transmitting the COVID-19. THE CANADIAN PRESS/Adrian Wyld
Canada’s top doctor warns full vaccination does not equal full protection from COVID-19

Post-inoculation, Theresa Tam says the risk of asymptomatic infection and transmission is far lower but not obsolete

The dash cam footage, taken May 7 at 8:18 a.m. belonged to the driver of a southbound vehicle that recently travelled out of the tunnel. (Reddit/Screen grab)
VIDEO: Dash cam captures dramatic rollover crash on Highway 99

Only one person sustained injuries from the collision, says B.C. Ambulance Services

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

Chevy stranded on a ledge above a rocky canyon at Mimi Falls near Logan Lake, April 28, 2021. (Photo credit: Margot Wikjord)
Police officer and fire chief team up in risky rescue of stranded dog near Logan Lake

Chevy, a rescue dog, needed rescuing again after getting stuck on a ledge above rocky canyon

Police were on the scene of a fatal shooting in Abbotsford. (Black Press Media files)
B.C. government to give more than $8 million for programs to curb gang violence

221 not-for-profit projects led by local governments and school districts among others will receive a one-time grant

Gord Judson steers his log truck down a forest service road, using two-way radio and call signals to mark his position for oncoming traffic. (B.C. Forest Safety Council)
Planning some B.C. wilderness fishing? Don’t catch a log truck

Remote recreation areas bracing for heavy pandemic pressure

Most Read