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

Just Posted

Coldstream Fire Department was quick to arrive and knock down a fire Sunday, May 16, in a Matner Lane orchard just up the hill from the firehall on Aberdeen Road. (Jennifer Smith - Morning Star)
Coldstream fire crews quick to knock down blaze

Fire broke out just before 2:30 p.m. on Matner Lane, which is just up the hill from the firehall on Aberdeen Road

Crews battled a grass fire behind the Tolko mill along the railway tracks off Otter Lake Cross Road in Spallumcheen Monday, April 26. (Caitlin Clow - Morning Star file)
Reports of man lighting Vernon fires with blowtorch

Grassfires sparked near train tracks, behind bottle depot

Frame Custom Homes, based in Kelowna, won top prize, design Excellence, at the Canadian Home Builders' Association's 2021 digital gala May 7, 2021, and best detached custom home over 5,000 square feet for Lakeside Haven in Vernon. (Contributed)
Builder’s custom Kelowna, Vernon homes win national prize

4 bed, 6 bath Vernon home complete with pool, putting green and elevator a Lakeside Haven

A number of undercover RCMP vehicles were spotted at a residence off Westside Road the morning of Tuesday, May 18. (Contributed)
UPDATE: One in custody following Westside firearm standoff

There is no longer a risk to the public but RCMP remain on scene

Christie Tujik (clockwise), Philipp Gruner, Julie Melanson and Jenelle Brewer are vying for a seat on the Vernon School Board. (Contributed)
Vernon school trustee candidates face off in forum

Voters in Vernon, BX and Silver Star can join May 18 virtual meeting

A prowling coyote proved no match for a stray black cat who chased it out of a Port Moody parking lot Friday, May 14. (Twitter/Screen grab)
VIDEO: Little but fierce: Cat spotted chasing off coyote by Port Moody police

The black cat is seen jumping out from under a parked car and running the wild animal out of a vacant lot

WorkSafe BC is out in the Interior making sure wineries, cideries and breweries are adhering to COVID-19 safety protocols. (File photo)
WorkSafe visiting Interior wineries, cideries and breweries ahead of tourist tasting season

40 field inspections and 35 consultations are expected over next few weeks

B.C. RCMP released these two photos of Erick Fryer (left) and Carlo Fryer (right). The two brothers from Kamloops were found dead near a remote road in Naramata May 10, 2021. (RCMP photo)
Slain Kamloops brothers found near Penticton not likely connected to recent B.C. gang wars: RCMP

Police confirm the bodies found near Naramata as Erick Fryer, 29, and Carlo Fryer, 31

Several RCMP cruisers stationed out front of Kelowna’s Global Fitness following a shooting on the morning of Monday, March 29. The shooting was later revealed to be gang-related. (Michael Rodriguez/Capital News)
B.C.’s top gangs are operating in Kelowna: RCMP

‘We have all of the major gangs in Kelowna,’ said Supt. Kara Triance

Kelowna RCMP precinct. (Michael Rodriguez/Capital News file)
Kelowna RCMP promotion process tainted with bias: federal judge

An officer was passed over for a promotion in 2015

A restaurant server on White Rock’s Marine Drive serves customers on a roadside patio. Indoor dining and recreational travel bans have been in effect since late March in B.C. (Peace Arch News)
B.C.’s COVID-19 infection rate falls to 411 cases Tuesday

360 people in hospital, up slightly, two more deaths

The Banff National Park entrance is shown in Banff, Alta., Tuesday, March 24, 2020. THE CANADIAN PRESS/Jeff McIntosh
Minister asks Canadians to camp carefully in national parks as season starts

Kitchen shelters in Banff National Park closed, trails on Vancouver Island will only be one-way

Names of those aboard the ship are seen at Komagata Maru monument in downtown Vancouver, on Tuesday, May 18, 2021. The City of Vancouver has issued an apology for its racist role in denying entry to 376 passengers aboard a ship that was forced to return to India over a century ago. Mayor Kennedy Stewart says discrimination by the city had “cruel effects” on the Sikhs, Hindus and Muslims aboard the Komagata Maru, which arrived in Burrard Inlet on May 23, 1914. THE CANADIAN PRESS/Darryl Dyck
Vancouver mayor says sorry for city’s role in turning away South Asians in 1914

Kennedy Stewart has declared May 23 as the annual Komagata Maru Day of Remembrance

A crew of WestCoast WILD Adventures employees tackled an onslaught of litter left at the ‘Locks of Love’ fence at Wally Creek on May 2. (Anne-Marie Gosselin photo)
Litter woes consume popular ‘Locks of Love’ fence on B.C.’s Pacific Rim

Popular view spot near Tofino plagued by people hanging masks and other unwanted garbage

Most Read