Something I learned about in my 3y as a social scientist embedded in a vaccine research ctr is AEFIs: Adverse Events Following Immunization. Lots of things happen after we’re vaccinated & the vast majority happen no more than they do at other times. (Thread) https://twitter.com/helenbranswell/status/1351038552994435073

Some things, like sore arms, happen more after an injected vaccine (in the arm) and that’s almost certainly caused by the vaccine. Other things, like, say, fevers, may happen more after a vaccine and many but not all are likely due to the vaccine.

Whenever a serious AEFI happens we want to investigate to see if we can figure out whether it’s due to a vaccine. Death is one of the most serious AEFIs but is usually not caused by vaccination. How do we know?

Sometimes it’s obvious. Dying as a passenger in a car accident is not because you had a vaccine the day before, for ex. But other times it’s harder, such as dying from, say, a stroke. Then experts have to look into it.

I am not an expert in causality, but some if the questions we have to ask when looking into serious AEFIs are: Is there a plausible mechanism? (For the car accident, no. For other things maybe; depends on the vaccine & AEFI.) Does the timing make sense? (Did the AEFI start...

...before vaccination, for example an infection.) And, importantly, in large groups of people, do we see this AEFI more often following vaccination than we do at other times or in unvaccinated people?

This last Q is super important if we get past the first 2, meaning that we can’t rule out that the AEFI might be caused by vaccination based on plausibility & timing alone.

It can be super scary to hear that someone died, or had a stroke, or developed a neurological disorder, following vaccination. But if they are just as likely (or more likely) to experience that without vaccination, the timing is almost certainly coincidence.

The vaccine scientists with whom I worked were very serious about AEFIs. They monitored seasonal flu shot AEFIs nationally every year just in case there was a “bad batch” or other problem. They believed that vaccination was overall fantastic but knew that...

People make & administer vaccines, and people can make mistakes. They wanted to ID and recall any potential “bad” vaccines before they hurt people or damaged public faith in vaccination (bad here meaning more risky than acceptable/usual, not necessarily more risky than disease).

They also followed people who had experienced serious AEFIs (fir ex, anaphylaxis) to understand whether they would recur if vaccinated again. I was very reassured by getting to “look under the hood” at these safety processes.

I can’t say all vaccine researchers or all countries’ safety surveillance systems are the same. But what I am saying is that AEFIs are real, can be scary, but aren’t always due to vaccination itself, and that there are some great scientists working to understand them better. /fin

Oh, and vaccine scientists, please correct me if I misspoke or anything I wrote could use clarification in your expert eyes!