Risk of Blood Clots : COVID versus Vaccines

"They're acting the way they [regulators and advisory committees] would if it were normal times. We're not in normal times. And I think they need to take that into account."

"I don't think they're responding the way they need to in a plague that's killing many thousands of people every month [globally]."

"They need to be very careful about how they send messages, meaning any message they send should begin with the death rate, hospitalization rate and burial rate for COVID for the week they're making the announcement."

Arthur Caplan, bioethicist, head, division of medical ethics, NYU School of Medicine, New York City 

"Confirmation of the first Canadian case of a COVID vaccine-induced blood clot was] kind of historic."

"Canada felt like it was protected from this, because it hadn't happened here."

"[Blood clots following inoculation are concerning] -- very concerning, don't get me wrong -- [but they're rare]."

"The work now being done is, how is it that this vaccine can induce these antibodies, and what is it about those few individuals who had this happen?"

Ishac Nazy, director, McMaster University Centre for Transfusion Research laboratory, Hamilton

Oxford researchers ran a study of COVID-19 patients

A new study recently released before publication out of Oxford University researchers reveals that COVID-19 is up to ten times likelier to cause a rare brain blood clot than would any of the current vaccines. Vaccines analyzed to confirm that they carry roughly the same remote blood clot risk; four in one million, to five in one million -- irrespective of whether it is the AstraZeneca, the Pfizer or the Moderna vaccine.

The U.S. Food and Drug Administration has placed a pause on doctors making use of the Johnson & Johnson vaccine, out of an "abundance of caution". This, at a time that Canada is expecting a shipment of up to ten million doses of the J&J vaccine. The FDA was motivated to act following reports that six women between the ages of 18 and 48 -- days after being vaccinated with the J&J vaccine -- had suffered a rare type of blood clot. Approximately 6.9 million Americans have already been vaccinated with the J&J vaccine. One among that blood-clot-group of six women died and another remains in critical condition.

Most provinces in Canada have now suspended the use of AstraZeneca for people under age 55, on the advice of the National Advisory Committee on Immunization, which is now considering whether to update its recommendation. All involved regulators and advisory committees in light of the uncertainties and new revelations relating to COVID and vaccines coming to the fore, are reacting cautiously and conservatively.

The situation is a delicate one at a time of steeply rising case counts of coronavirus among the general public and the suspicions that blood clots have raised in the public mind raises a risk of seriously setting back vaccination campaigns. A reported 80 percent refusal rate for AstraZeneca's vaccine is now standard in Italy. France has seen public confidence plummet for the vaccine, while Germany and Spain have as well. So it is not surprising that reports are emerging of Canadians refusing the vaccine in the face of authorities pleading with the public to "take the first shot offered".

This week, Health Canada continued to express confidence in its approval of AstraZeneca and J&J vaccines for all ages, following a review of available data. Dr.Supriya Sharma, chief medical adviser, places the risk of a clotting with AstraZeneca at one in 250,000. Independent advisers with Health Canada are in the process of reviewing whether to modify their no-one-under-55 recommendations for AstraZeneca in light of "substantial uncertainty" of benefits against that age group's risks.

 

A man is inoculated with the AstraZeneca Covid-19 vaccine at a vaccination centre in the Catalonia Railway Museum. File photograph: David Ramos/Getty Images

 

People are lacking the information they need to be enabled to make informed personal decisions. They require data that will inform them how large the risks from continuing to vaccinate are, versus risks from pausing. According to the Oxford researchers, the COVID risk for cerebral venous thrombosis (CVT) -- a clot in the cerebral vein responsible for draining blood from the brain -- is some eight times greater than with the Oxford/AstraZeneca vaccine, those under 30 included.

Professor of psychiatry at the University of Oxford, Paul Harrison and his study co-authors state comparisons must be cautiously interpreted "since data are still accruing". Based on an electronic health record network with a total of 81 million people in the United States, researchers counted the number of CVT cases that came to light in two weeks after a diagnosis of COVID -- following the first dose of a vaccine.

CVT -- according to their estimates, occurred in 39 out of one million patients. In people receiving Pfizer or Moderna vaccines, the risk was 4.1 per million, whereas CVT has been reported in five per million following a first dose of the AstraZeneca-Oxford vaccine. The McMaster Platelet Immunology Laboratory tests blood samples sent in from doctors, for antibodies whose presence can activate platelets leading to clotting. The lab forms part of a national surveillance system for vaccine-induced blood clots. 

 

What remains unclear is why it is that females seem at particular risk. A Quebec woman to date is the country's only confirmed case. She is recovering at home. What also remains as yet elusive is what it is that triggers the production of the clotting antibodies.

As per an official statement by Oxford University, the number of CVT cases diagnosed in the two weeks following diagnosis of COVID-19, or after the first dose of a vaccine. (REUTERS)

"[Health Canada's advisers are reviewing whether to modify no-one-under 55 position for
AstraZeneca in view of] substantial uncertainty [of the benefits given risks for that age group while preparing recommendations for the Johnson & Johnson vaccine]."

"Are they looking at different information when they should be sharing the data? If there's one government federal system, a single entity that is making that decision, they need to get their act together. If people are confused, it's because they're not doing their job."

"This is a situation where experts communicate badly and blame the audience."

"It's not that hard for officials to find out what information people need and give it to them in clear, concise terms. How are the authorities weighing those two risks [blood clots and risks from pausing]? How good is their information? How soon will it be better?"

"[Research shows people want the truth] It also shows that they can understand the critical facts if care is taken in drafting and testing the messages. It's not that hard."

Baruch Fischhoff, risk communication expert, Carnegie Mellon University, Pittsburgh