No trend found between Covid-19 vaccine blood clots and age-sex factors
Rare fatal blood clots after Covid-19 vaccines do not appear to be affected by sex or age, according to a new study by the UK’s independent Drug Safety Research Unit (DSRU).
Key highlights:
- Researchers at the DSRU have analysed all UK cases of TSS that were reported to the MHRA following Vaxzevria, and calculated case fatality rates by age and sex.
- Of 443 recorded TTS cases, 81 cases were fatal (18.28%) and case fatality remained stable throughout the observation period at 17-18%.
- The study found no trends in deaths by age or by sex, though they did observe that events more frequently occurred following someone’s first dose of the vaccine.
Unusual clotting with concurrent low platelets, known as thrombosis with thrombocytopenia syndrome (TTS), after adenoviral vector vaccines including the Covid-19 vaccine AstraZeneca (Vaxzevria) was first reported in Europe in March 2021, when it was thought younger women may be at increased risk. Risk minimisation measures, including restrictions on age, were introduced in several countries.
Now, researchers at the DSRU have analysed all UK cases of TSS that were reported to the Medicines and Healthcare products Regulatory Agency (MHRA) via the Yellow Card scheme following Vaxzevria, and they have calculated case fatality rates by age and sex.
Researchers analysed data reported between 12 May 2021 and 25 May 2022 when a total of 443 cases of TTS were recorded. Of these, 81 cases were fatal (18.28%) and case fatality remained stable throughout the observation period at 17-18%.
The study found no trends in deaths by age or by sex, though they did observe that events more frequently occurred following someone’s first dose of the vaccine.
Samantha Lane, senior research fellow at the DSRU, who led the research, said: “Context is important here. Our research focused on a very rare adverse reaction after a certain type of Covid-19 vaccine. The benefits of all Covid-19 vaccines far outweigh any risks.
“Our research is part of on-going work to find out more about new drugs and vaccines, and how to make them even safer. In this case, there has been global concern that younger women might be more at risk of TSS, a rare form of blood clot, after adenoviral vector Covid-19 vaccines. But our research found no trends by age or by sex. This is good news. Though more research is needed to find out what does increase someone’s risk, so we can then put measures in place to protect them.”
By May 2022, 24.9 million first doses of Vaxzevria had been administered in the UK, as well as 24.1 million second doses. It’s estimated there were 15.74 cases of TSS (most of which were not fatal) per million first doses of Vaxzevria and 2.12 cases per million second doses.
The study, called ‘Assessing Case Fatality on Cases of Thrombosis with Thrombocytopenia Following COVID-19 Vaccine AstraZeneca (Vaxzevria) in the United Kingdom: A Review of Spontaneously Reported Data’ has been published in Drug Safety.
The DSRU is an independent and internationally renowned research unit that monitors, studies and communicates the safety and risk management of medicines.