Most of western Europe has temporarily paused the rollout of the AstraZeneca vaccine as a precautionary measure following concerns the vaccine could be linked to blood clots.

But Associate Professor Bartlett, of HMRI and the University of Newcastle, said there was "no data" to show any causal link between vaccination with the AstraZeneca COVID-19 vaccine and clotting.

"It does look very much like these are associated events that have happened at a known rate, and certainly the rate in which these clotting events are occurring is no higher than it normally is," he said. "Personally I think there was no need to pause it. Millions of people have now received these vaccines. Safety has been closely monitored."

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But he said there was a "slightly higher" risk of anaphylaxis for people who were already susceptible to severe "type 1 hypersensitivity" allergic reactions.

"In flu vaccine, anaphylaxis rates are between one and 10 per million," he said. "The Pfizer and AstraZeneca vaccines are closer to about 100 in a million. These vaccines are stimulating a more robust immune response on vaccination. I think the recommendations will be that those people will need additional medical supervision - they may need to go to a more specialised site for their vaccination to ensure they can be appropriately monitored and medical treatment is right on hand. No one has died from this."

Associate Professor Bartlett said anyone who has had an allergic reaction or anaphylaxis after their COVID-19 vaccine had responded immediately to adrenaline and recovered.

"With all vaccines, allergic reactions or anaphylaxis is a risk, and we are fully prepared to treat anyone who experiences that. It is a type 1 hypersensitivity, so it would happen very, very quickly.

"It's like a mosquito bite. We know that within minutes of being bitten by a mosquito you begin seeing a red swelling and itchiness. That's essentially - on a larger scale - what we're monitoring for when we are vaccinating.

"These are amazing medical breakthroughs that are really going to change the way we live again, and we all need to be on board."

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