COVID Vaccine Blood Clot Risk Explained As Shot Blamed for BBC Host Lisa Shaw's Death

After radio presenter Lisa Shaw who worked for the BBC in England died at the age of 44 in May, a coroner ruled Thursday that her death was due to "complications of an AstraZeneca COVID vaccination."

According to the BBC, Newcastle coroner, Karen Dilks, said it was "clearly established" that her death was due to a very rare "vaccine-induced thrombotic thrombocytopenia"—a disorder characterized by clots forming in small blood vessels and a low platelet count.

In Shaw's case, she developed blood clots in her brain, eventually resulting in her death.

Dr. Tuomo Polvikoski, a consultant neuro-pathologist who examined Shaw after her death, told the BBC the incident was "surprising" given that she had a history of being fit and healthy.

The U.K. Medicines and Healthcare products Regulatory Agency (MHRA) chief safety officer, Dr. Alison Cave, said the benefits of the Oxford-AstraZeneca vaccine, which has not yet been authorized for use in the United States, continue "to outweigh the risks for most people."

What Are the Risks of Blood Clots Following COVID-19 Vaccination?

According to the MHRA, the agency had received 417 cases of major blood clot events in the U.K. following AstraZeneca vaccinations as of August 18, 2021. These cases included 72 deaths, six of which occurred after the second dose.

By this point, around 24.8 million first doses and 23.9 million second doses of the vaccine had been administered in the U.K., indicating that the risks are very low.

A largest-of-its-kind study published on Thursday in the BMJ found an increased risk of thrombocytopenia (a condition characterized by low platelet counts,) blood clots in veins and, other rare arterial blood clots in short-time intervals after a first dose of the AstraZeneca vaccine.

In addition, the authors found an increased risk of blood clots in arteries and ischaemic strokes—which happen when a blood clot blocks the flow of blood and oxygen to the brain—after a first dose of the Pfizer-BioNTech vaccine

The study also found an increased risk of rare blood clots in the brain known as cerebral venous sinus thrombosis (CVST) after a first dose of both vaccines, but in this case the numbers were very small and further confirmation is needed, according to the authors.

The authors said the risks of blood clots were "much lower" than those associated with COVID-19 itself.

While people can develop blood clots without having been infected or vaccinated, the authors said there would be an estimated 934 extra cases of thrombocytopenia for every 10 million people after infection with SARS-CoV-2, compared with 107 after a first dose of AstraZeneca.

Meanwhile, they found that there would be an estimated 1,699 extra cases of ischaemic strokes for every 10 million people after SARS-CoV-2 infection, compared to 143 after a first dose of the Pfizer vaccine.

The risks associated with the vaccines are also relatively short-lived, according to the BMJ study. The paper's lead author, Julia Hippisley-Cox, professor of clinical epidemiology and general practice at the University of Oxford, said in a statement:

"People should be aware of these increased risks after Covid-19 vaccination and seek medical attention promptly if they develop symptoms, but also be aware that the risks are considerably higher and over longer periods of time if they become infected with SARS-CoV-2."

Earlier in 2021, the European Medicines Agency reported at least 169 possible cases of CVST among 34 million recipients of the AstraZeneca vaccine; 35 possible cases among 54 million recipients of the Pfizer vaccine; and five possible (but unvetted) CVST cases among 4 million recipients of the Moderna mRNA vaccine.

The Johnson & Johnson (J&J) vaccine has also bee associated with an increased risk of some types of rare blood clots. Figures from the U.S. Centers for Disease Control and Prevention (CDC) show that as of April 12, 2021, there had been six reports of CVST in the United States following around 6.8 million doses administered. This suggests an incidence rate of less than one per million doses administered.

The CDC also previously said that as of April 23, 2021, after more than 8 million doses of the J&J vaccine had been administered, there had been 15 reports of women who developed a condition known as thrombosis with thrombocytopenia syndrome (TTS). This is a serious condition that involves blood clots with low platelets.

The figures suggest a very low but increased risk of TTS one to two weeks after vaccination with the J&J shot.

"These reports represent a reporting rate of seven such events per one million vaccinations among women 18 through 49 years old and a rate of 0.9 per 1 million vaccinations among women 50 years and older," the CDC said.

"For all women, this is a rare adverse event. For women 50 years and older and men of all ages, the adverse event is even more rare."

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Stock image showing a coronavirus vaccine. Is there a risk of blood clots following COVID-19 vaccinations? iStock