Scientists have found clues as to why AstraZeneca’s vaccine could cause blood clots

Doctors may have discovered why AstraZeneca’s COVID-19 vaccine can cause life-threatening blood clots in very rare cases.

The discovery, made in a pair of reports published in the magazine’s online edition on Friday New England Journal of Medicine, could be the key to the global deployment of AstraZeneca’s vaccine, help develop effective treatments for the side effect and provide clues on how to perfect the vaccine to address the problemexperts say.

But it could also hamper efforts to get the vaccine approved in the United States, where three vaccines are already available.

The AstraZeneca vaccine seems to cause some people to develop antibodies that target a protein in the human body called platelet factor 4 (PF4), which triggers the action of platelets and activates a coagulation cascade, explained report co-author Dr Theodore Warkentin, professor of molecular medicine and pathology at McMaster University in Ontario, Canada.

“It’s an antibody that the vaccine activates in one way or another, and in some circumstances it causes unusual blood clottingWarkentin pointed out.

The phenomenon is similar to a rare pharmacological side effect caused by heparin, an anticoagulant, and is known as heparin-induced thrombocytopenia, Warkentin noted.

The vaccine’s coagulation side effects are so rare that the European Medicines Agency (EMA) and the UK Health Products and Medicines Regulatory Agency have decided to keep it on the market, concluding that its benefits outweigh its risksAstraZeneca noted in a statement.

However, the vaccine label will be updated to mention blood clotting as an extremely rare potential side effect.

“AstraZeneca has been working very actively with regulators to implement these changes in product information, and is already working to understand the individual cases, the epidemiology and the possible mechanisms that could explain these extremely rare events,” he said. he noted.

Until April 4, the EMA has received reports of 169 cases of brain clots and 53 cases of abdominal clots among some 34 million doses of AstraZeneca that have been administered across Europe, according to Reuters.

In the UK, 19 people have died from serious vaccine-related blood clots, CNN reported.

Cases of clots look like what is sometimes reported with heparin anticoagulant

Two of the three COVID-19 vaccines that are distributed in the United States (Pfizer and Moderna) have not shown such side effects. But on Friday, European drug regulators said they were examining reports of rare blood clots in four people who received the Johnson & Johnson COVID-19 vaccine. Of the four cases, three occurred in the United States during the vaccine deployment and one person died, and the fourth case was reported in a clinical trial, according to CNBC.

One of the new AstraZeneca vaccine reports focuses on 11 patients from Germany and Austria who developed serious bleeding problems after being vaccinated, while the other looked at the cases of five healthcare workers , aged 32 to 54, who developed the side effect.

The tests revealed that all of the patients developed PF4 blood clotting complexes similar to those caused by heparin, although none of them received the anticoagulant.

These new discoveries they still do not give doctors clues about people who may become ill from excessive clotting after receiving the AstraZeneca vaccine, noted Dr. William Schaffner, professor of infectious diseases at Vanderbilt University Medical Center in Nashville, Tennessee.

“So far it’s focused on younger age groups, but we can’t determine in advance who these people are. The question will be, as we pursue public policy around the world, how will this vaccine be managed? Schaffner said.

But the findings could help guide treatment for people who develop symptoms similar to heparin-induced thrombocytopenia, Warkentin said.

“If someone develops symptoms five or more days after the vaccine, whether it’s a headache or neurological symptoms, or abnormal pain or shortness of breath, then the person who received the vaccine would know to see a doctor.Warkentin pointed out. “It is equally important that clinicians assessing the patient know how to look for them.”

Treatment may already be available, based on how doctors would treat an even rarer type of heparin-induced thrombocytopenia, Warkentin said.

Heparin directly affects PF4 to cause clotting, but in some cases the drug promotes an autoimmune response that affects the important protein, Warkentin said.

Doctors treat heparin-induced autoimmune thrombocytopenia by giving high doses of intravenous immunoglobulin, which floods the body with healthy antibodies to muffle the signal produced by the drug, Warkentin said.

The future of the AstraZeneca vaccine is uncertain

“We recommend that when a physician recognizes such a patient with this new condition, called vaccine-induced immune thrombotic thrombocytopenia, you are treated not only with anticoagulation but also with high doses of this intravenous immunoglobulin.Warkentin advised.

Now that AstraZeneca knows what’s going on causing the side effect, you also have an opportunity to review the makeup of the vaccine and how it’s done to find out what’s going on, Warkentin said.

“There might be a way to find out what it could be and maybe a way to manipulate the vaccine to make it safer.Warkentin noted.

Schaffner noted that these reports “implicate the vaccine as the immune initiator of a very rare event that creates antibodies that involve platelets, those tiny elements in the bloodstream that cause clotting.”

Ministries of health around the world will now have to weigh this information against the risks posed by COVID-19, Schaffner explained.

“This is particularly relevant because this vaccine is very inexpensive, can be manufactured in large quantities and can be managed in a normal cold chain. At first it was actually made public and predicted that this would be perhaps the most important vaccine for use in many developing countries, ”Schaffner said. “I think now a lot of health departments are going to do a cost benefit analysis.”

AstraZeneca was preparing to seek emergency use authorization in the United States for its vaccine, but this news casts a shadow over this initiative, Schaffner added.

“I haven’t heard the opposite, but you have to ask yourself if the company wants to go through the process,” he said. “It seems that here in the United States we have, at the moment, a large number of vaccines, our three vaccines having an emergency use authorization. In some parts of the country, our vaccine supply exceeds demand. The need for a fourth vaccine has been drastically reduced ”.

Dr Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases, also cast doubt on the prospects for the AstraZeneca vaccine in the United States.

“We have already contracted enough vaccines with Moderna and Pfizer and [Johnson &Johnson]Fauci told CNN. “There are no plans to immediately start using the [vacuna] AstraZeneca even if approved by emergency clearance, which is possible ”.

Posted by HealthDay News for The New York TImes

Read on: