COVID-19 Vaccines and Blood Clots

Why have European countries paused their Astrazeneca rollout?

Gideon M-K; Health Nerd


Pictured: Gotta love vaccines! Source: SELF Magazine

Edit 6/04 with new data about the MHRA and EMA investigations into these clots and the Astrazeneca vaccine.

Edit 8/04: The EMA has now confirmed that a link between the Astrazeneca vaccine and these rare clot conditions is likely. In other news, I had my Astrazeneca vaccine last week.

Vaccines are amazing, life-saving innovations, and the COVID-19 vaccines are no different. As with any medical procedure, there are potential drawbacks to using them, but we know from massive pieces of scientific research that the COVID-19 vaccines are both safe and effective.

And yet, as you have probably heard on the news, for one specific vaccine most of Europe has stopped their rollout. Rather than giving millions of people the Astrazeneca/Oxford (AZ) vaccine against COVID-19, a dozen countries have decided to stop vaccinating due to fears of side-effects.

Pictured: Ducks. Not a known side-effect of vaccination, but they are definitely cute. Source: Pexels

So I thought I would explain what’s happening, and why you probably don’t need to worry even if you’ve had the AZ vaccine.

How It All Works

The basic idea of vaccine rollouts is simple. You exclude common and dangerous side-effects in clinical trials, and identify all the common and moderate ones as well like headaches and pain at the vaccine site. However, even with mammoth studies, with 10,000s of people in them, it’s impossible to exclude things that happen really rarely. If a side-effect only happens to 1 in 200,000 people who get the vaccine, you’d need a clinical trial including literally millions of individuals to be certain to catch it in the numbers.

This raises an issue — we give vaccines at a population level, after all. Something that happens to 1 in 200,000 people might sound incredibly rare, and it is, but it will also happen dozens of times if you vaccinate 80 million people. And remember, it is vitally important to most of Europe that they vaccinate as many people as quickly as possible, given the vast COVID-19 outbreaks across the continent.