06 December 2021

A £1.6 million British study has been launched to investigate why there are rare cases of blood clotting with low platelets among people vaccinated against COVID-19.

In March 2021, small numbers of people who had received the AstraZeneca vaccine were admitted to hospital with blood clots in the major veins in the brain, abdomen, or elsewhere in the body, but at the same time having a low level of platelets. The condition is known as thrombotic thrombocytopenia syndrome (TTS).

So researchers from 11 institutions led by the University of Liverpool, who will be supported by teams within the NHS and national agencies, will study the mechanisms underlying TTS and its incidence amongst vaccine recipients and COVID-19 patients.

This project is supported by the National Institute for Health Research and is backed by £1.6 million of government funding from the Vaccine Taskforce.

Chief investigator Professor Sir Munir Pirmohamed said: “The combination of blood clots with low platelet levels is very rare, and although it has been reported previously - including before the pandemic - the clusters of cases were unusual and an association with the vaccines was suggested.

“It is important to note that the vast majority of individuals given the vaccine do not develop TTS - but between 1 in 100,000 and 1 in a million do. We do not yet understand why a vaccine that is safe for almost everyone can cause TTS in particular individuals.

“Our research will help understand why COVID-19 vaccines can lead to TTS in rare cases.”

The project will investigate how common TTS was before the emergence of COVID-19, as well as in those who have been vaccinated against COVID-19 and in those suffering from the virus.

It also aims to understand why a very small number of those vaccinated against COVID-19, as well as those with the virus, develop blood clotting disorders. Finally, the team will investigate the changes in the body that lead to the unique combination of blood clots and low platelet count seen in TTS.

Professor Andy Ustianowski, NIHR clinical lead for the COVID-19 Vaccination Programme and Joint National Infection Specialty Lead, said: “The benefit of COVID-19 vaccines still far outweighs the risks, but it’s important we understand more about the biology behind TTS and why COVID-19 vaccines can lead to it in these rare cases.

“This research is vital to help find some answers to prevent and treat TTS, and further improve the safety of current and future vaccines.”

Dr June Raine, MHRA chief executive, added: “We welcome this important study. Whilst reports of blood clots together with low levels of platelets are extremely rare, understanding more about what has caused this very rare condition will allow us to further improve the safety of COVID-19 vaccines.

“We ask those who suspect they have experienced any side effect linked with their COVID-19 vaccine to report it to the Coronavirus Yellow Card website. This provides vital safety information needed to carry out our work.”

Source: University of Liverpool

Link: https://news.liverpool.ac.uk/2021/11/30/1-6m-study-aims-to-understand-why-covid-19-vaccines-can-lead-to-rare-instances-of-blood-clotting-with-low-platelets/

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