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Why the UK changed covid-19 AstraZeneca vaccine advice for under-30s


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The UK has restricted the use of the Oxford/AstraZeneca covid-19 vaccine in some age groups

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Today the UK effectively restricted use of the Oxford/AstraZeneca covid-19 vaccine to people aged 30 and over because of the risk of a rare blood clot syndrome. But other European countries and Canada have broader restrictions, with higher age cut-offs. Why are the regulations different, and what are the implications for vaccine roll-out in the UK?

What are the safety concerns over the Oxford/AstraZeneca vaccine?
UK and European medicines regulators have been reviewing a small number of people who developed blood clots linked with low levels of platelets – small particles in the blood that normally help in clotting – soon after having the Oxford/AstraZeneca vaccine. Both have now concluded that they are possibly caused by the vaccine, although they say the benefits of vaccination for most people outweigh the risks of catching covid-19.

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How should people under 30 weigh the benefits and drawbacks?
For healthy people under 30, the risks from catching covid-19 are low, although there may also be a slightly higher rate of the blood clot condition in younger people too. So, the UK Joint Committee on Vaccination and Immunisation (JCVI) has said that the equation is “more finely balanced” for this group. That means that for people under 30, the chance of the vaccine causing the clotting reaction is a little greater than the likelihood of avoiding severe illness from covid-19.

Why are other countries setting the age limit higher?
Canada and France have restricted the Oxford/AstraZeneca jab to people 55 and over, while Germany has set the bar at 65, and Iceland 70. These countries seem to have taken a more cautious, broad-brush approach, reasoning that the blood clots have generally been seen in middle-aged people so the vaccine should be withheld below a certain age until we know more. The JCVI, by contrast, today announced results of a detailed analysis, comparing the risk of the suspicious blood clots with the risk of getting badly ill from covid-19 for every age group in ten-year bands. This is why the Committee set the age limit at 30.

How will this affect people under 30?
Jonathan Van-Tam, England’s deputy chief medical officer, said at a press conference on 7 April that people under 30 in the UK will be offered an alternative covid-19 vaccine, either the one from Pfizer/BioNTech or Moderna, which started being used in the UK this week. This should not delay them getting a vaccine by more than a few weeks, as the UK should have enough supplies by the time under-30s are offered the jab, he said.

“I am assured that because of our supply situation, the effect on the timing of our overall programme should be zero, or negligible,” said Van-Tam, adding that the Johnson & Johnson vaccine is also likely to become available at some point.

How about people over 30 who have not yet received a vaccine?
The JCVI is adamant that the benefits outweigh the risks for these older age groups because the blood clots are so rare. Across all age groups, by the end of March there had been 79 cases reported in the UK, out of more than 20 million doses given of the Oxford/AstraZeneca vaccine – a rate of about four in a million. A breakdown by age groups has not been released.

Are women at higher risk?
Apparently not. More cases of the blood clots have been reported in women – 51 of the 79 cases in the UK. But that seems to be because this vaccine has been given to more women; most healthcare workers and care home staff are female. “If you look at the incidence rate according to the number of vaccines administered, there’s actually no difference between men and women,” says Munir Pirmohamed, chair of the UK’s Commission on Human Medicines.

What about under-30s who have already had one dose of the Oxford/AstraZeneca vaccine?
They should have the second one when it is due, says the JCVI. People under 30 who have already had their first dose were prioritised because they were at higher risk for medical reasons or due to their occupation. That means their risk level is higher than a typical person in their twenties and so the risk-benefit equation tips back towards getting the jab. In addition there is no evidence yet on the safety or effectiveness of mixing vaccine types. “We would be voyaging into an evidence-free zone if we [made] those kind of changes,” says Anthony Harnden, deputy chairman of the JCVI.

What is causing these blood clots?
We don’t yet know. The blood clot syndrome – which has been termed vaccine-induced prothrombotic immune thrombocytopenia or VIPIT by scientists in Germany – could involve an immune response against platelets, triggered by the vaccine. Perhaps antibodies made against the vaccine also react to a protein on the surface of platelets, speculates Beverley Hunt, medical director of Thrombosis UK.

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