Oxford/AstraZeneca: Why the vaccine's benefits far outweigh any risks

Credit: PA

Even the largest clinical trials can’t include enough people to spot extremely rare side effects that might be caused by new drugs and vaccines.

It’s why the best drug watchdogs around the world have “yellow card” schemes where doctors are encouraged to report any events in their patients following the use of a new drug or vaccines. And when they say “any” they mean it.

Skimming through the UK data for possible events linked to Pfizer and AstraZeneca vaccines, they include everything from cancer diagnoses, and heart attacks to sunburn and broken arms and legs.

  • Tom Clarke reports on the latest developments as European nations halt the AZ vaccine rollout

It’s a dangerous cocktail of data. Dangerous because, viewed out of context, it can suggest there might be problems where there are none.

Dangerous because in the middle of a pandemic when, based on all available evidence, the disease you’re vaccinating against is far more deadly than the theoretical side effect of a vaccine you might be worried about.

To avoid this pitfall, what the regulators are looking for is in this data are patterns. And, so far, in the data for the UK and the EU as a whole there is no pattern of dangerous side effects.


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There’s abundant evidence of side effects, some quite severe, for both AstraZeneca and Pfizer vaccines, including flu-like symptoms, joint pain, excessive tiredness. But they are generally short-lived and not life threatening.

But the much rarer, and much more serious, events are not — so far at least — showing clear patterns.

The most compelling piece of evidence here is that none is happening at a higher rate in people vaccinated than what you’d expect to see in the population before vaccination.



The events reported independently by several European countries in response to the AstraZeneca vaccine are concerning.

They centre around cases of lethal, or potentially lethal blood clots in younger people (in which blood clots are typically rare) combined with a low level of blood platelets (a condition called thrombocytopenia).

This is a bit baffling as platelets are the factor in our blood that cause the blood to clot. Normally these two things don’t go together.

The government has just got a huge delivery of the AstraZeneca jab Credit: PA

For that reason, it’s very understandable that these events would be given the yellow card. And very important that they are investigated.

But they’re occurring at rates of tens of cases out of millions of cases of people vaccinated. They’re way down in the realms of statistical uncertainty. If there were no Covid pandemic, there wouldn’t be much debate.

The vaccine should be paused while thorough investigations take part: a review of cases combined with with lab experiments and big epidemiological studies. But in the presence of an indisputably dangerous virus, the as-yet-to-be-determined risk of a vaccine is crushed by the weight of evidence for the vaccines’ effectiveness at preventing deaths.

It’s why our regulator the MHRA, the European regulator the EMA and the World Health Organisation have reviewed the available evidence and shared it among themselves and are still firmly of the opinion that the benefits of the vaccine outweigh any risks as far as they can be determined.

Ten of our neighbours have suspended their roll-outs of the Oxford/AstraZeneca jab out of an “abundance of caution”. But what about the far greater abundance of risk? Every day that their Covid vaccinations are suspended thousands of lives across Europe are put in danger.