AstraZeneca Vaccine Faces Uncertainty as EU Acknowledges Possible Link to Rare Blood Clots, Yet Affirms Benefits Outweigh Risks

On the 7th, the European Medicines Agency announced that thrombosis accompanied by low platelet counts should be listed as a rare side effect of the AstraZeneca vaccine. On the same day, the World Health Organization stated that a causal link between vaccination with the AstraZeneca vaccine and the occurrence of thrombosis was considered “plausible but not yet confirmed.” Due to concerns about potential thrombosis risks, some European countries have called for cautious use of the AstraZeneca vaccine in certain populations. However, both the European Medicines Agency and the World Health Organization pointed out that thrombosis following AstraZeneca vaccination is “very rare,” and the overall benefit-risk balance remains positive.

European Medicines Agency

Identification of "Rare" Side Effects

Sabine Straus, Chair of the Pharmacovigilance Risk Assessment Committee (PRAC) of the European Medicines Agency (EMA), stated at a press conference on the 7th that thrombosis accompanied by thrombocytopenia is a “very rare” side effect of the AstraZeneca vaccine. The specific risk factors triggering this adverse reaction remain unconfirmed, and the Committee is conducting further investigations into the matter.

Emer Cooke, head of the European Medicines Agency, stated that the mortality rate from COVID-19 infection is far higher than the risk of death from rare side effects caused by vaccination; therefore, overall, the benefits of this vaccine in preventing COVID-19 outweigh its side effects.

In a statement released on the day, the European Medicines Agency (EMA) stated that as of March 22, it had received reports of 62 cases of cerebral venous sinus thrombosis and 24 cases of splanchnic vein thrombosis in its database, with 18 deaths among all these cases. During the same period, approximately 25 million people in the EU and the UK had received this vaccine. Most patients who developed thrombosis were women under the age of 60, with symptoms appearing within two weeks after receiving the first dose of the vaccine. The EMA recommended that individuals experiencing shortness of breath, chest pain, leg swelling, abdominal pain, neurological symptoms, or petechiae within several weeks of receiving the AstraZeneca vaccine should seek medical attention immediately.

EU health ministers held a video conference on the evening of the 7th to discuss the use of the AstraZeneca vaccine. While the meeting did not reach a consensus on issuing unified recommendations, it called on EU member states to strengthen coordination to address public hesitancy toward receiving the AstraZeneca vaccine.

World Health Organization

“Possibly causal but not yet confirmed”

The World Health Organization stated on the 7th that a causal link between vaccination with the AstraZeneca vaccine and the occurrence of blood clots is considered “plausible but not yet confirmed.”

The World Health Organization’s Global Advisory Committee on Vaccine Safety stated in a press release that although thrombotic events are concerning, they are extremely rare. Among approximately 200 million recipients of the AstraZeneca vaccine worldwide, only a small number of thrombotic events have been reported. However, the committee also indicated that it will continue to collect and evaluate follow-up data.

The committee pointed out that it is normal to discover potential adverse events following vaccination during large-scale immunization campaigns across countries. This does not necessarily mean these events are related to the vaccination itself, but they must be investigated to ensure any safety concerns are promptly addressed. Like all medications, vaccines have side effects. The use of vaccines is based on a risk-benefit analysis.

As multiple recipients of the AstraZeneca vaccine developed blood clots, several European countries briefly announced a suspension of its use in early March. The European Medicines Agency subsequently determined that the benefits of the AstraZeneca vaccine outweighed the risks, prompting nearly all EU member states to resume its deployment, with some countries imposing additional restrictions.

National Trade-offs

It is recommended to suspend use in certain populations.

UK: The UK Medicines and Healthcare products Regulatory Agency stated on the 7th that, based on the latest analysis, healthcare professionals should only consider administering the AstraZeneca vaccine to individuals at higher risk of thrombosis when it is clear that the protective benefits outweigh the potential risks.

The agency stated that, based on the latest data, the likelihood of developing thrombotic symptoms after receiving this vaccine remains “very low,” with approximately four cases per million vaccinees in the United Kingdom. The agency indicated that individuals who experienced related thrombotic symptoms after receiving the first dose of this vaccine should not proceed with the second dose.

Italy: The Italian public health authorities recommend that the AstraZeneca vaccine be administered exclusively to individuals aged 60 and above, while those under 60 who have already received the first dose may still proceed with the second dose.

Belgium: On the 7th, health authorities at all levels of government in Belgium unanimously decided to suspend the administration of the AstraZeneca vaccine to individuals under the age of 56.

Finland: The head of the health department in Helsinki, Finland, stated that some individuals aged 65 and older were disappointed upon arriving at vaccination sites to find they would be receiving the AstraZeneca vaccine, with some ultimately choosing not to get vaccinated.

Bulgaria: On the evening of the 7th, the Bulgarian Drug Agency recommended that women under the age of 60 exercise caution when receiving the AstraZeneca vaccine; individuals who have received the first dose of the AstraZeneca vaccine should postpone administration of the second dose.

Spain: On the afternoon of the 7th, the Spanish Ministry of Health and the major autonomous communities reached an agreement to suspend the administration of the AstraZeneca vaccine to individuals under the age of 60, restricting its use exclusively to those aged 60 to 65.

Estonia: The head of the Estonian Government’s Scientific Advisory Committee stated on the 7th that Estonia has suspended the administration of the AstraZeneca vaccine to individuals under the age of 60.

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UK Pediatric Clinical Trials Suspended

University of Oxford in the UK announced on the 6th local time that it has suspended clinical trials for vaccinating children and adolescents with the AstraZeneca COVID-19 vaccine in the UK, pending further guidance from pharmaceutical regulatory authorities regarding the use of this vaccine.

On the 6th, the University of Oxford confirmed in a statement that it had suspended a small-scale clinical trial in the UK involving the administration of the AstraZeneca vaccine to children and adolescents. The University of Oxford and AstraZeneca PLC are jointly developing a COVID-19 vaccine, and in February, they announced their intention to recruit 300 participants aged 6 to 17 years in the UK.

In a statement, the University of Oxford said that the clinical trial “had no safety issues,” but it would wait for further information from the UK Medicines and Healthcare products Regulatory Agency before resuming the trial.