Why is the UK offering under-30s an alternative to the AstraZeneca vaccine?

Ministers have said that the vaccine is safe at all ages and that the decision was driven by "an abundance of caution". 

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The government sought to reassure the public this morning (8 April) about the safety of the AstraZeneca vaccine. The Health Secretary Matt Hancock has said that the jab is "safe at all ages" and that the decision to give under-30s an alternative vaccine had been driven by an "abundance of caution".

Hancock emphasised that the government is being led by the science. Like the European Medicines Agency (EMA), the UK's Medicines and Healthcare products Regulatory Agency (MHRA) had not recommended age restrictions on the vaccine. But the MHRA said its review of "extremely rare [...] specific blood clots with lowered platelets has concluded that the evidence of a link with Covid-19 Vaccine AstraZeneca is stronger but more work is still needed".

The government hopes that giving under-30s the option of an alternative will maintain public confidence in the vaccine programme, which is among the most effective globally and has already averted thousands of deaths. 

How small is the risk of blood clots?

Following the administration of more than 20 million AstraZeneca jabs in the UK, there have been 79 cases of blood clots alongside low levels of platelets. Among those 79 cases, 19 people have died, including 13 women and six men. Approximately four people in a million (or one in 250,000) have developed blood clots according to the MHRA and fewer than a quarter of those have died. The likelihood of dying due to a blood clot in the UK after taking the vaccine is therefore one in a million.

To put those numbers into context, the vaccine programme is believed to have averted 6,000 deaths in the first three months of the year alone, and the total number of people who have been killed by Covid-19 in the UK is more than 120,000. You are, according to BMJ data cited by Politico, four times more likely to be hit by a plane crashing into your home than to die of a blood clot after receiving the vaccine.

So why is the government offering under-30s an alternative vaccine?

As health officials have reminded the public this week, no medicine is without risk. The MHRA has said that its review indicated there is a "slightly higher incidence" of blood clots "reported in the younger adult age groups" and that this should be "taken into account when considering the use of the vaccine".

It appears that the government feared that some younger people would have concluded that the risk of taking the AstraZeneca jab was higher for them than not doing so, and would therefore decline to be vaccinated at all, leaving them at risk of serious illness. But the MHRA was keen to emphasise on Wednesday (7 April) that it did not recommend imposing age restrictions on the vaccine, and neither has the EMA, which is why...

... the government isn't preventing under-30s from getting the AstraZeneca vaccine

The NHS will be required to offer adults in the youngest age range – 18-29 – the option of an alternative vaccine. But they will still be able to choose the AstraZeneca vaccine over those produced by Pfizer, Moderna and others, if the AstraZeneca jab is available earlier, and some doctors may encourage them to do so. Matt Hancock said today that the government would have sufficient stocks of alternative jabs to meet the targets for vaccinating the under-30s.

Are there risk factors?

Although the Joint Committee on Vaccination and Immunisation (JCVI) has stated that there are no official risk factors, the incidence of blood clots is twice as high in women. Some scientists have speculated that this may be linked to the use of hormone replacement therapy and the contraceptive pill. A recent study in the Lancet suggested that each year around one in 2,000 women suffer from a blood clot while taking the combined oral contraceptive pill. Women who take the pill are therefore 125 times more likely to suffer a blood clot than the average person in the UK who has taken the AstraZeneca jab.

The government has not routinely given vaccines to pregnant women and doctors have been advised to discuss the risks individually; this advice remains unchanged. People who have already received a first dose of the AstraZeneca vaccine should take a second dose – there are no reports of blood clots among those who have received their second dose. The JCVI advises "that all individuals offered a Covid-19 vaccine should be fully informed about the benefits and risks of vaccination".

What are the warning signs of a blood clot?

The head of the MHRA, Dr June Raine, has said that "as a precautionary measure we would advise anyone with a headache that lasts for more than four days after vaccination, or bruising beyond the site of vaccination after a few days, to seek medical attention". She added that "mild flu-like symptoms remain one of the most common side effects of any Covid-19 vaccine, including headache, chills and fever. These generally appear within a few hours and resolve within a day or two, but not everyone gets them." The MHRA, Raine added, plans to continue monitoring "all the data we have on this extremely rare possible side effect".

[See also: Stephen Bush on how the government’s vaccine communications strategy is leading to dangerous headlines]

Oscar Williams is a senior journalist at the New Statesman covering technology.

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