Greater risk of developing blood condition from Covid than vaccine

Astrazeneca Covid-19 vaccine may be linked to a very slight increased risk of a rare blood condition, a study led by Edinburgh University has found.

The condition, known as idiopathic thrombocytopenic purpura (ITP), is characterised by low platelet counts, and can lead to bleeding or blood clots.

Researchers say the chance of developing ITP after receiving the vaccine is still lower than that of developing it because of Covid-19, and that it should not deter the roll out of the vaccine programme.

The increased risk is estimated to be 11 per million doses, similar to figures for Hepatitis B, flu and MMR vaccines.

The same risk was not found for the Pfizer vaccine, also included in the research.

The study of 5.4 million people in Scotland, of whom 2.5 million had received their first vaccine dose, is the first analysis of ITP, clotting and bleeding events following vaccination for an entire country.

The Medical and Healthcare products Regulatory Agency (MHRA) had previous reported low platelet counts in combination with blood clots after Astrazeneca vaccination, estimated at about 13 per million first doses.

Experts say the new study’s specific findings about ITP are likely to be a manifestation of this general condition. The MHRA is actively monitoring the situation.

Researchers were unable to establish a definitive link between other forms of clotthe ting – including the rare form called cerebral venous sinus thrombosis or CVST – due to the very low number of cases in vaccinated people included in the study.

Those at most risk from ITP tended to be older, and with least one underlying health condition such as coronary heart disease, diabetes or chronic kidney disease.

The research team, led by Edinburgh University, and including Aberdeen, Strathclyde,glasgowandstandrew’s Universities,analysedadataset as part of the EAVE II project, which uses anonymised linked patient data to track the pandemic and the vaccine roll out in real time.

They also also looked at health records dating back to September 2019 to investigate any previous issues with ITP, clotting or bleeding disorders.