AstraZeneca Vaccine Thrombosis Saga Continues with No Clear Answers

AstraZeneca_Nathan Stirk/Getty Images

Nathan Stirk/Getty Images

The European Medicines Agency (EMA)’s head of vaccines, Marco Cavaleri, believes there was a clear link between the AstraZeneca-Oxford COVID-19 vaccine and blood clots. 

“In my opinion, we can say it now, it is clear there is a link with the vaccine,” Cavaleri told Italy’s Il Messaggero Newspaper.

It’s not clear, however, what causes the blood clots. But he may be one of only a few who believes there is a connection.

In mid-March, more than a dozen countries suspended the deployment of the AstraZeneca-Oxford University vaccine after incidences of blood clots were reported. Per data received as of March 8, 17 million people in the European Union and the United Kingdom had received the vaccine and there had been 15 cases of deep vein thrombosis and 22 cases of pulmonary embolism. 

Incidences were first reported in Denmark and Norway, which halted distribution, followed by Germany, France and other countries. Germany’s Health Minister Jens Spahn admitted it was a “very low risk” but would be above average if it was actually linked to the vaccine.

On March 14, AstraZeneca issued a statement, noting, “A careful review of all available safety data of more than 17 million people vaccinated in the European Union (EU) and U.K. with COVID-19 Vaccine AstraZeneca has shown no evidence of an increased risk of pulmonary embolism, deep vein thrombosis (DVT) or thrombocytopenia, in any defined age group, gender, batch or in any particular country.” In fact, the company pointed out, “This is much lower than would be expected to occur naturally in a general population of this size and is similar across other licensed COVID-19 vaccines.”

As of March 22, Health Canada indicated that it had not received any reports on blood clots in the country. The warning label tells people to seek immediate medical attention if they develop shortness of breath, chest pain, leg swelling, or persistent abdominal pain after receiving an AstraZeneca shot. Health Canada also indicated it has evaluated the available data and determined that the AstraZeneca vaccine is not associated with an increased risk of thrombosis.

There is very little consensus country to country on whether the vaccine is linked to announced cases of blood clots. Andreas Greinacher and his group at Germany’s Greifswald University Hospital are studying it in Germany and Austria and think that an overactive immune response is what is causing the rate of blood clots in a few vaccinated people.

“This is looking for the needle in the haystack,” Greinacher told The Washington Post

The U.K. is supporting the homegrown vaccine, which was developed jointly by Sweden and U.K.-based AstraZeneca and the University of Oxford. France, Germany, Sweden, and Canada are restricting its use in younger people. Denmark and Norway have still completely paused the use of the AstraZeneca-Oxford vaccine.

AstraZeneca stated that “patient safety remains the company’s highest priority” and noted that no link between the vaccine and blood clots had been identified by the U.K. or European regulators. They are continuing to study their databases to determine if the incidences of blood clots are occurring more than they would be in the normal patient population.

The primary concern is over cases of cerebral venous sinus thrombosis (CVST), a rare vein clot that causes brain bleeds. Britain’s data suggests an incidence of about 1 in 500,000 vaccines. But there appear to be slightly higher rates in countries that began using the vaccine only among younger people. The EMA said it is investigating about 44 cases of rare brain clots and a minimum of 14 deaths among 9.2 million vaccinations in 30 countries in Europe.

Those numbers suggest 4.6 cases for every 1 million shots within a few weeks after vaccination. That’s generally higher than expected over a short period of time, experts note. According to Johns Hopkins, brain clots would normally affect about five people per 1 million over 12 months.

For the Pfizer vaccine, which is more broadly distributed in Europe than the AstraZeneca vaccine, there appear to be brain clots of about 0.2 per million after vaccine and zero for the Moderna vaccine. The European numbers do not include Britain or cases from other countries after March 22. Germany’s regulator reported 31 cases of unusual blood clots in 2.7 million people receiving the AstraZeneca vaccine as of March 29, nine of whom died.

Up to March 21, Britain reported 30 cases of brain and other clots out of 18 million people receiving the AstraZeneca vaccine, with none reported for Pfizer. Norway’s regulators said the AstraZeneca vaccine “likely” caused clots in six medical workers out of 120,00 individuals vaccinated, with four deaths.

In India, the AstraZeneca vaccine is the primary shot being given, with more than 70 million doses having been administered since January. No cases of blood clots have been reported by Indian authorities to European regulators.

Generally speaking, EMA and the World Health Organization (WHO), and the British regulatory authority all are saying the benefits of the vaccines outweigh the risks, which are very rare, and encourage people to get their vaccinations.

However, German Chancellor Angela Markel did say the government “cannot ignore” the data, even if it damaged confidence in the vaccine. She believed it would be worse not to be transparent. “But what will erode confidence more? To sweep such a thing under the rug, not to take it seriously?”

And the data is still not clear, even on which age groups, if any, are most affected. Initially, reports suggested it was in the oldest patients, but others have suggested it is occurring in younger patients who would be unlikely to normally have brain clots. The data suggests, but isn’t clear, that the risk may be higher for women, although that is confounded by the ratios of women to men being vaccinated.

“If you look at who was being vaccinated in the European Union with the AstraZeneca vaccine back in January, February, and early March, there is about a 2-to-1 ratio of women to men,” said Peter Arlett, the EMA’s head of pharmacovigilance and epidemiology.

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