The European Medicines Agency (EMA) may have reached the expected decision to allow for the resumption of immunisation with AstraZeneca vaccines, but many questions remain to be answered.
The agency has determined the vaccine is safe and effective, and that its benefits in protection from Covid-19 outweigh any risks.
They have found that the vaccine is not associated with an increase in the overall risk of thrombo-embolic events or blood clots. In fact, there were fewer than expected events among the millions of people who have received the vaccine.
They have also ruled out any batch or quality control issues in relation to the small number of cases under review, where people suffered rare and unusual but very serious clotting disorders after being administered the vaccine.
But the EMA’s scientists were unable to definitively rule out a link between these cases and the vaccine.
The number of cases is tiny, roughly equivalent to one-in-a-million – 25 cases out of 20 million vaccine recipients. The reports examined come from four EU countries, India and the UK.
Compare this to the 100,000 people in the EU who suffer blood clots each month.
Yet there remains “some uncertainty”, as the EMA put it, around the cases of the two conditions involved. One is cerebral sinus vein thrombosis (CSVT), a rare type of stroke which can result in massive bleeding in the brain. Symptoms appeared seven to 14 days after immunisation. A number of these 18 cases have been fatal.
There have been seven cases of disseminated intravascular coagulation, in which blood clots form throughout the body, resulting in low platelet count. This can result in internal bleeding and damage the brain or other organs.
Younger women seem to be over-represented among the cases, but the EMA has said it is premature to conclude they are more at risk due to the background risk of thrombosis and differences in the population of people vaccinated.
Further investigations will also look at whether people previously infected with Covid-19 are at greater risk; the virus has been associated with clotting events in some patients. It will also look at whether there is any link with use of the contraceptive pill. The EMA says too it will examine the record of the three other authorised vaccines to see if similar issues have arisen; US authorities have reported some blood clotting events among people who have received other vaccines.
Although the events of the past week have disrupted urgently needed vaccine rollouts and unsettled many people, it is also evidence of the system working as it should. European regulators identified potential issues and the central EU regulator has investigated them. There are no certainties generally in medicine but it is only too clear, with Covid-19 cases rising once again in many parts of Europe, how much the vaccine is needed.
The EMA has said it plans further investigations into the cases identified. It has advised health professionals to be aware of the signs of these conditions in case they arise, and the patient information leaflet for the AstraZeneca vaccine will have to be amended.
People will be advised to seek prompt medical assistance if they get any of the following symptoms after vaccination:
- pain in the chest or stomach
- swelling or coldness in an arm or leg
- severe or worsening headache or blurred vision after vaccination
- persistent bleeding
- multiple small bruises.
The recommended changes are easily made but restoring full confidence in the vaccine is likely to prove more difficult.