The European Medicines Agency (EMA) and the UK Medicines and Healthcare products Regulatory Agency (MHRA) report that a possible link between AstraZeneca’s COVID-19 vaccine and a combination of blood clots and low blood platelets is very rare and reaffirm that the overall benefits of the vaccine in preventing COVID-19 outweigh the risks of side effects.

The EMA’s Pharmacovigilance Risk Assessment Committee (PRAC), the EMA committee responsible for the evaluation of safety issues for human medicines, concluded that unusual blood clots with low blood platelets should be listed as very rare side effects of AstraZeneca’s COVID-19 vaccine (now called Vaxevria). The PRAC noted that the blood clots occurred in veins in the brain (cerebral venous sinus thrombosis [CVST]), the abdomen (splanchnic vein thrombosis), and in arteries, together with low levels of blood platelets and sometimes bleeding.

Separately, the MHRA said that the incidence of these blood clots is very rare, and the benefits of vaccination continue to outweigh any risks, but it advises careful consideration be given to people who are at higher risk of specific types of blood clots because of their medical condition. As of March 31, 2021, 20.2 million doses of AstraZeneca’s COVID-19 vaccine had been given in the UK, which means the overall risk of these blood clots occurring is approximately four people in a one million who receive the vaccine. The MHRA said further evaluation is needed.

One plausible explanation offered by the EMA for the combination of blood clots and low blood platelets is an immune response, leading to a condition similar to one seen sometimes in patients treated with heparin (heparin-induced thrombocytopenia). EMA’s PRAC has requested new studies and amendments to ongoing ones to provide more information and said it will take any further actions as necessary.

The MHRA issued updated guidance for healthcare professionals on how to minimize risks as well as provide further advice on symptoms for vaccine recipients to look out for four or more days after vaccination.

The Australian Technical Advisory Group on Immunization (ATAGI) also notes further evidence of a rare but serious side effect involving thrombosis (clotting) with thrombocytopenia (low blood platelet count) following the vaccination of AstraZeneca’s COVID-19 vaccine. ATAGI and other Australian officials continue to consult with the World Health Organization, and UK, European, and other regulatory agencies in countries where use of the AstraZeneca COVID-19 vaccine has been widespread.

The Australian pharmaceutical company, CSL, and a manufacturing partner for the vaccine, has issued a statement that the company remains committed to meeting its contracted arrangements with the Australian government and AstraZeneca for locally produced AstraZeneca COVID-19 vaccines in Australia.

Source: European Medicines Agency, UK Medicines and Healthcare products Regulatory Agency, Australian Department of Health, and CSL