Regulators have been reviewing reports of ‘unusual blood clots with low blood platelets’ occurring in association with the use of certain COVID-19 vaccines, for example a rare but serious clot of the sinus vein that drains blood from the brain.
Based on all currently available information, the MHRA has recently concluded that there is a possible link between the Oxford-AstraZeneca COVID-19 Vaccine and the extremely rare, unlikely to occur, blood clots with low platelets. The EMA is also adding this to their emergency use authorisation’s (EUA) information as a very rare side effect “probably” caused by the AstraZeneca COVID-19 vaccine. The MHRA and EMA regulators will continue to monitor and evaluate blood clotting events reported with the vaccines, to determine the nature and level of the risk and to better understand the strength of the association between the Oxford-AstraZeneca vaccine and these rare clots (i.e. to determine whether or not these rare clots are definitely being caused by the vaccine). They are also providing updated advice on how to minimise the potential risks of these very rare clotting events. The MHRA and the EMA, and the World Health Organization, have concluded, based on all the currently available information, that the benefits of the vaccine outweigh the potential risks and outweigh the known risks of the vaccines and you should continue to receive the vaccine(s) when asked to do so unless specifically advised otherwise.
In the UK, as a result of the MHRA conclusion and weighing the balance of benefits and risks, currently the JCVI has concluded that for adults under 30 years of age who are not in a higher clinical risk group, it may be preferable to offer an alternative to the Oxford-AstraZeneca vaccine. This is a precautionary measure while additional evaluations and studies to better understand this potential risk of clotting are undertaken. Individuals aged 18 to 29 years who have received their first dose of AZ vaccine as part of the Phase 1 programme, without suffering any serious side effects, should complete their course with the same vaccine.
The EMA have not identified specific risk factors (such as age or gender) for these rare clots associated with the Oxford-AstraZeneca vaccine and continue to recommend that the vaccine has a positive benefit:risk balance for all age groups.
The identification of a “safety signal” for unusual blood clots with low blood platelets is testament to the effectiveness of the monitoring systems in place to detect potential safety risks with vaccines early on. These clotting events are so rare (as of 31 March 2021, approximately 4 people in a million who receive the vaccine) that the risk would not ordinarily have been detected in the large clinical trials which supported approval of the vaccines in current use. It remains important for any possible side effects for any of the COVID-19 vaccines to be reported to the regulator. Regulators will continue to conduct safety monitoring and evaluation to understand more about the clotting events and who might be affected. In the UK you can report suspected side effects to COVID-19 vaccines at https://coronavirus-yellowcard.mhra.gov.uk/.
This comment has been prepared by FPM with review by a panel of FPM experts in vaccines, medicines development and pharmacovigilance, including Dr Renata Crome, Dr Craig Hartford, Dr Gillies O’Bryan-Tear, Dr Sheuli Porkess, Dr Neil Snowise, Dr Penny Ward.