On 7 April, the UK effectively restricted use of the Oxford/AstraZeneca covid-19 vaccine to people aged 30 and over because of the risk of 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?
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 the clots are possibly caused by the vaccine, although they say the benefits of vaccination for most people outweigh the risks.
For healthy people under 30, the health risks from catching covid-19 are low, but there may be a slightly higher rate of the blood clot condition in younger people. So, the UK Joint Committee on Vaccination and Immunization (JCVI) has said the risk-benefit 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 risk of severe illness from covid-19.
Canada and France have restricted the Oxford/AstraZeneca jab to people 55 and over, while Germany has set the bar at 60, 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 they 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 10-year bands. This is why the committee set the age limit at 30.
England’s Deputy Chief Medical Officer, Jonathan Van-Tam, said at a press conference on 7th April that people under 30 in the UK will be offered an alternative Covid-19 vaccine, either the Pfizer/BioNTech one or the Moderna shot, which started being used in the UK this week. This shouldn’t cause more than a few weeks of delay for this age group, 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.
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 hasn’t been released.
It seems woman are more at risk of the side effects of the vaccine as 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.
Munir Pirmohamed, Chair of the UK’s Commission on Human Medicines says:
“If you look at the incidence rate according to the number of vaccines administered, there’s actually no difference between men and women.”
People under 30 who have already had their first dose were prioritized because they were at higher risk of falling ill with Covid-19 for medical reasons or due to their occupation. That means their risk level is higher than a typical person in their 20s 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.
Anthony Harnden, Deputy Chairman of the JCVI says: “We would be voyaging into an evidence-free zone if we made those kinds of changes.”
The medical community says they don’t know yet what causes the blood clot.
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.
Beverley Hunt, Medical Director of Thrombosis UK, speculates that perhaps antibodies made against the vaccine also react to a protein on the surface of platelets.
The most common side effects are of the AstraZeneca are:
Pain or tenderness at the injection site
Muscle or joint aches
Other less common side effects are also possible.