There have been no cases of blood clots linked to the AstraZeneca vaccine since under-40s were advised to get a different jag.
In May people under the age of 40 began having either Pfizer or Moderna vaccines.
This is due to a very rare but slightly increased risk of developing vaccine-induced immune thrombotic thrombocytopenia (VITT) – otherwise known as blood clots.
Researchers have not seen any new cases of VITT in the three to four weeks leading up to mid-August.
‘No cutting corners’
Prof Neil Mabbott is a professor of immunopathy at Edinburgh University.
He explains: “This highlights the very careful monitoring of potential serious side effects from vaccines.
“Soon after we started distributing them to the wider population, occasional very rare but serious side effects such as these blood clots, associated with reduced platelets, were encountered.
“The decision was made not to give the vaccine to younger people.
“Removing those who were at very slim risk of developing that side effect, you would expect to see this decrease, and that’s exactly what we’re seeing.
“We should take this as reassuring that corners aren’t being cut and the safety of these vaccines is taken very seriously.”
‘Benefits outweigh the risk’
It is not yet known why, otherwise healthy, younger people were more susceptible to VITT. Research is under way to determine the cause.
Prof Mabbott continues: “When we do the original safety study, these are in much smaller numbers of individuals.
“We couldn’t wait for 29 million people to be vaccinated before we decided whether they’re safe or not.
“They are run in much smaller trials. But if you only have 10,000 people in a trial, you’re unlikely to detect a very rare side effect if it has an incidence of one in 100,000.”
News around vaccine-induced blood clots has led to increased hesitancy among some still to have the jag.
How does this compare to other jags?
But Prof Mabbott wants to get the message across that coronavirus vaccines are safe, effective and being closely monitored.
He says: “Up until now, we haven’t administered vaccines on such a global scale and collected such data on a daily basis about side effects etc.
“It is my opinion we’d see a very similar situation if we looked in depth at a similar roll out of another vaccine on the same kind of scale.
“The Covid vaccines, I believe, carry no more serious side effects than other vaccines we’re already rolling out.
“After tens of millions of doses in the UK and billions around the world, evidence is by far showing benefits, and protection the vaccine provides against Covid-19, far outweigh any potential very rare side effects.
“The quicker everybody becomes fully vaccinated in the UK and around the world, the easier it will be to open up society to what we were used to before the pandemic.”