Link between AstraZeneca COVID vaccine and rare blood clots confirmed

Pharma News: The European Medicines Agency’s (EMA) safety committee (PRAC) has concluded that unusual blood clots with low blood platelets should be listed as very rare side effects of Vaxzevria (formerly COVID-19 Vaccine AstraZeneca).

According to the Therapeutic Goods Administration (TGA), there has been one case reported in Australia that is very similar to the cases reported in Europe and the United Kingdom. The clinical details of this case are currently under review by the TGA.

Dr Roger Lord, senior lecturer with the Faculty of Health Sciences at The Australian Catholic University and Visiting Research Fellow with The Prince Charles Hospital in Brisbane, said “The announcement by the European Medicines Agency (EMA) must be kept in perspective. Vaccine safety is of the utmost importance and the EMA and other regulators (TGA, FDA) do need to investigate this adverse event while acknowledging the difficulties of linking cause and effect with new vaccines.

“The Pandemrix vaccine for the 2009 H1N1 influenza (swine flu) pandemic was associated with an increased rate of narcolepsy in children. Initially, it was the adjuvant used to boost the immune response that was suspected as the cause then the interaction between Pandemrix and the H1N1 virus itself. After more than 10 years no specific linkage between the vaccine and the adverse event has been confirmed.

“Being able to link this rare adverse event to use of the AstraZeneca vaccine may, like the Pandemrix vaccine, prove to be inconclusive. It is however very important to highlight that the risk of developing a serious blood clot are incredibly small compared to risk of possible COVID-19 infection,” he added.

EMA is reminding healthcare professionals and people receiving the vaccine to remain aware of the possibility of very rare cases of blood clots combined with low levels of blood platelets occurring within 2 weeks of vaccination. So far, most of the cases reported have occurred in women under 60 years of age within 2 weeks of vaccination. Based on the currently available evidence, specific risk factors have not been confirmed.

The PRAC noted that the blood clots occurred in veins in the brain (cerebral venous sinus thrombosis, CVST) and the abdomen (splanchnic vein thrombosis) and in arteries, together with low levels of blood platelets and sometimes bleeding.

The Committee carried out an in-depth review of 62 cases of cerebral venous sinus thrombosis and 24 cases of splanchnic vein thrombosis reported in the EU drug safety database as of 22 March 2021, 18 of which were fatal. The cases came mainly from spontaneous reporting systems of the EEA and the UK, where around 25 million people had received the vaccine.

“One plausible explanation 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, HIT). The PRAC has requested new studies and amendments to ongoing ones to provide more information and will take any further actions necessary,” the EMA said.

The PRAC stresses the importance of prompt specialist medical treatment. By recognising the signs of bloods clots and low blood platelets and treating them early, healthcare professionals can help those affected in their recovery and avoid complications.

“The risk of mortality from COVID is much greater than the risk of mortality from these rare side effects,” said the EMA’s executive director, Emer Cooke.