UK, EU may be wrong on AstraZeneca vaccine

When it comes to Covid-19 vaccinations, Britain has been a bit of a renegade. At the outset of the global rollout, the UK — in an effort to inoculate as many people as possible as quickly as possible — started its campaign by lengthening the time interval between the first and second shots beyond what was indicated from trials.
Instead of a recommended gap of as little as three weeks for the Pfizer Inc-BioNTech shot or six to 12 for the one developed by AstraZeneca Plc and the University of Oxford, the government stretched the interval to 12 weeks for all cases. It was a risky gamble that invited criticism from health experts and analysts who worried the untested move might lead to subpar protection and enable the generation of virus variants.
Thankfully, the gamble paid off: The campaign has gone amazingly well, helped in part by the simultaneous four-month hard lockdown that helped reduce infection rates and lower the risk that vaccine-resistant variants would evolve.
Britain’s scientists and policy makers should be applauded for getting the country to a very low infection rate despite the gradual easing of restrictions. Now, though, the UK is again breaking from the pack over vaccines in a way that poses fresh risks. Except this time, the pack may be misjudging risks, too.
Britain is only slightly restricting the Astra vaccine’s usage, recommending those under 30 not get the shot. That’s a substantially lower age than that of every other Western European country despite the potentially higher rate of rare blood clots (now called thrombosis with thrombocytopenia syndrome, or TTS) in younger people. All of these countries have access to the same data regarding the rates of these rare clotting events and can make the same calculations when it comes to the risk-benefit ratio. So who is right? May be both are wrong.
In making risk-benefit assessments about vaccines, you need to take into account background infection rates, because they can help determine whether the risk of side effects outweighs that of developing disease. When there’s a higher rate of infection, the risk of severe Covid also increases, and that can help justify the lesser risk of taking a vaccine that may cause side effects. When infection rates are low and the risks aren’t as disparate, the opposite is true. This is the crux of the issue.
Both the UK’s Medicines and Healthcare Products Regulatory Agency and the European Union’s European Medicines Agency have released infographics showing this interplay. At low infection rates, such as those currently in the UK, the MHRA shows that rare clots from the vaccine occur at a rate of 0.8 per 100,000 for the 30-to-39 age band, compared with a 2.7-per-100,000 rate of being admitted to an intensive-care unit with Covid. There is a difference, for sure. But it’s not as great as the difference when infection rates are higher. In several European countries, the rate of ICU admittance is 24.9 per 100,000.
Given its low infection rates, the UK is taking too much risk with the Astra vaccine. It should raise the age cutoff to the over-55 population, where the relative risk of clots is 0.4 per 100,000 compared with a 10.5-per-100,000 risk of ICU admission. And it should do so even if that means a delay in some reopening measures.

—Bloomberg