Should I worry about having my next Astrazeneca jab?
Following new research on blood clots, Miranda Levy looks at the latest guidance on second vaccines
I’ve booked my cut-and-colour for Wednesday and an alfresco lunch this afternoon. But the invitation that’s on my mind the most right now? The text from the NHS to inform me that it’s time for my second Covid jab. Six weeks ago, I received my first vaccination. I’m 52 and, like most people my age, had the Oxford Astrazeneca. I was overjoyed. Now, though, after the events of last week, and with my second dose looming, even ardent pro-vaxxers like me are starting to ask a few questions.
Research is continuing into the possibility of a (vanishingly small) risk of blood clots after the Astrazeneca jab. Up to March 21, the Medicines and Healthcare products Regulatory Agency (MHRA) received 79 complaints of blood clots accompanied by low platelet count, in all people who had received their first dose of the vaccine, out of 20 million doses given. Of the 79 people, 19 died. The MHRA said blood clot side-effects are “very rare” and “being detected in an extremely small number of people’. The cause of these deaths has not been definitively established.
Last Wednesday, the Joint Committee on Vaccination and Immunisation (JCVI) announced that people under 30 will now be offered different vaccines. “We decided that the risk-to-benefit ratio didn’t really stack up when it came to the very well under 30s,” says Anthony Harden, deputy chairman of the JCVI. “As a precautionary approach, we would advise an alternative vaccine for that particular age group.”
I’ve been more than aware of the political battles rumbling in Europe over the Astrazeneca jab, but now British experts are shifting views, too. Even Jonathan Van Tam, the lovable Deputy Chief Medical Officer with the homely metaphors, has admitted some caution, saying of the vaccine rollout: “This is a course correction.”
So the 18 to 29s will be offered a different jab when their turn comes later this summer. But what of those of us not in that age group who are waiting for our second Astrazeneca jab now? After all, the German regulators have advised that under-60s who have received their first dose of this vaccine should be given a second dose of the rival Pfizer or Moderna, and France has now followed suit, advising under55s to do the same. Various European countries have restricted use of the jab for younger people.
Britain’s regulator said last week that the benefits of the jab still far outweigh the risks for the majority of people, and anyone who has had a first Astrazeneca jab should continue with it for their second.
So should we be worried – and what happens when you mix and match jabs? “The chances of dying from a blood clot caused by a vaccine are similar to the chances of being struck by lightning,” says Tim Spector, professor of genetic epidemiology at King’s College, London and leader of the Zoe Covid symptom app, which logs the experience of more than four million contributors globally. “And the chance of catching Covid each week is now down to one in half a million, when, at the peak of the pandemic, it was one in 50.”
“These figures are not being put into context,” he says. “The risk of vaccine blood clots is extremely rare. We have data on 600,000 Astrazeneca loggers, and we haven’t yet seen a severe clotting case.” Indeed, the chance of getting a blood clot from the jab is about one in 250,000 and the risk of dying after a vaccine in all ages is less than one in a million, based on UK data analysed by regulators. “Although the numbers are tiny, you are slightly more likely to have these rare events if you are under 60,” says Prof Spector. “But you are much more likely to have a side-effect from Covid, that is likely to be more severe, and even fatal.”
Add to this the risk of long Covid, with symptoms that include breathlessness, fatigue and cognitive impairment. “Up to 10 per cent who develop Covid are getting long-term
‘These figures are not being put into context. The risk is extremely rare’
symptoms,” says Anthony Harden of JCVI. “Long Covid is more prevalent in old people, younger women, and those with a higher BMI. So it’s still a very important vaccine for those individuals under the age of 30, as it is for everybody in the population for different reasons.”
Experts stress that it’s vital to return for your second vaccine dose. According to a paper published in The Lancet in January, the Astrazeneca jab offers protection of 64 per cent after at least one standard dose. This compares to just over 70 per cent if you have had two full doses.
But if there is even the tiniest risk of something sinister happening – and the link has not yet been proven – would it not make sense to switch to another vaccine? Can you “mix and match” (known in the trade as “heterologous prime-boosting”)? Right now, the consequences of doing so are “unknown”, according to Prof Spector. There are currently a number of trials investigating this approach, including the COM-COV trial in the UK (mixing Astrazeneca and Pfizer) and a largescale study in China. They have not yet reported their results.
The concept of mixing different types of vaccines is not new: it was done in the case of Ebola, for example. And the Covid vaccines do work differently: Astrazeneca is based on the injection of a disabled chimpanzee cold virus, while Pfizer uses a fundamentally different technology to produce spike proteins in the body. In fact, many experts are in favour of mixing them.
“Immunologically, there are several arguments in favour of heterologous priming,” says Dr Jakob Cramer, the head of Vaccine Development organisation CEPI. Other scientists agree that this mixing will become “essential”.
“In future, everyone will be mixing and matching,” agrees Prof Spector. “It’s inevitable, and we need to get used to it. In fact, this is probably a good thing. Mixing vaccines could mean broader protection over new variants. As each vaccination triggers slightly different immune responses, it will be harder for the virus to mutate. Moderna and Johnson & Johnson are on their way, as are around 20 others.”
Experts across the field are joining in to support the Astrazeneca jab. “The benefits of the jab far outweigh the risk,” says Prof Wei Shen, the chair of JCVI. “Those who have received their first Astrazeneca should continue to be offered the second dose of Astrazeneca according to the schedule.”
As for me, I am feeling entirely reassured. In fact, my main concern about going back for “round two” had always been rather less dramatic. My strong response to the first jab knocked me out for the best part of two weeks, with headaches and temperature spikes, and slight fatigue that persisted for a month.
But, according to Prof Spector’s data, second time around for we Astras tends to bring fewer side-effects. Pfizer seems to be the converse. So, when I get the call, there I will be, with my arm stuck out, waiting for (almost) perfect immunity.