A paramedic prepares doses of the AstraZeneca vaccine for patients at a walk-in COVID-19 clinic at a Buddhist temple in the Smithfield suburb of Sydney on Aug. 4, 2021.

Saeed Khan | AFP | Getty Images

A new study has provided further details on the “rare but devastating” blood clotting complications associated with the Oxford-AstraZeneca Covid-19 vaccine.

In a peer-reviewed article published Wednesday in the New England Journal of Medicine, Massachusetts Medical Society scientists analyzed the first 220 cases of the disease reported in the UK.

The Oxford-AstraZeneca vaccine – now one of the most widely used Covid vaccines in the world – was launched in the UK in January, making it the first country to give the vaccine.

A very small number of people who were vaccinated with the AstraZeneca vaccine have developed blood clots. Described by health officials as “extremely rare”, it is characterized by blood clots accompanied by low platelet counts.

The Massachusetts Medical Society study uses data identified from 294 patients who presented to UK hospitals between March 22nd and June 6th.

All of these patients had received their first dose of the Oxford-AstraZeneca shot and were hospitalized with symptoms between five and 48 days after their vaccination. The average time between vaccination and hospitalization was 14 days, the results showed.

The overall mortality rate for VITT in the study was 22%.

The researchers also found that 41% of patients who presented with VITT were not diagnosed with any underlying health problems. Of those who reported a past or current illness, the study found that there were no prevalent diseases or medications that were “unexpected in the general population”.

“Against the background of a successful vaccination program in the UK, VITT has emerged as a rare but devastating complication,” the study’s authors said in their report. “We found that it often affects young, otherwise healthy vaccine recipients and is associated with high mortality.”

“In our cohort, 85% of the patients were younger than 60 years, although the (Oxford / AstraZeneca) vaccination was predominant in older adults,” the scientists found.

As a precaution, Great Britain has been offering people under 40 an alternative to the Oxford AstraZeneca vaccine since May.

People diagnosed with VITT were between 18 and 79 years old, with the mean age being 48, the study showed.

As of July 28, inclusive, an estimated 24.8 million first doses of the Oxford-AstraZeneca Covid vaccine had been administered in the UK, with an estimated 23.6 million second doses received.

On July 28, government figures show that for every million first or unknown doses of the Oxford AstraZeneca shot, 14.9 people developed a rare blood clot with low platelet counts. After a second dose of the vaccine, the number dropped to 1.8 cases per million.

The overall death rate for that period was 18%, the government data showed, with 73 deaths. Six of these occurred after the second dose.

Late last month, AstraZeneca published a study that found the VITT rate was 8.1 per million after the first dose of its vaccine, which dropped to 2.3 per million after a second dose.

According to official information, 411 suspected cases of VITT had been reported in Great Britain by July 28.

Benefits vs. Risks

In a statement Thursday, AstraZeneca said the research published in the New England Journal of Medicine was drawn from “a small sample size”.

“Recent practical evidence from millions of people shows that AstraZeneca’s vaccine has a similar safety profile to other vaccines and that thrombosis with thrombocytopenia is extremely rare and treatable,” said a spokesman.

The spokesman added that the infection with Covid-19 “poses a far greater risk” for rare blood clotting events.

“Vaccines remain the most effective protection against Covid-19 and the best way out of this pandemic,” they said.

Both the UK and EU drug regulators have identified possible links between the Oxford AstraZeneca vaccine and rare blood clots.

In April, the company announced it would comply with government requests in the UK and Europe to update its Covid vaccine labels. However, it stressed that the WHO had said “a causal relationship is considered plausible but not confirmed”.

The UK Joint Vaccination and Immunization Committee has stated time and time again that for the vast majority of people, the benefits of the Oxford-AstraZeneca vaccine continue to outweigh the risks.

Several health authorities, including the WHO, the European Medicines Agency and the International Society on Thrombosis and Hemostasis, agree that the benefits of giving the vaccine outweigh the risks.