Thread by @BarclayBenedict

Yesterday we were shown various slides comparing risks of rare side effects of AZ jab and Covid in different age groups. At first sight they look nice, but really they raise as many questions as they answer.

THREAD

The first issue is the incidence they use, which is 2 per 10,000 people for "low prevalence". They don't say what time frame that refers to, but they give a hint: roughly UK in March. UK in March reported around 80 per million per week, or 0.8 per 10K.

That's less than 2, but assuming that slightly over half of cases are missed, we can assume incidence is per 7 days. However, that raises a new issue. The rate is now half that, and falling fast. So really, the current risk of contracting Covid is much lower than they're assuming

That reduces the real risk on the Covid side of the graph, but there is a factor that pulls in the other direction - they give the number of ICU admissions avoided per 16 weeks. Why 16? Vaccine continues to protect after that, but risk of Covid remains.

In the end, the Covid risk depends massively on how we deal with the virus over the coming months and years, and could be far lower or far higher. It depends on policy at a much wider level.

There are other issues too. The Covid risk given is the average per age group, but we know risks vary greatly by underlying conditions. For a healthy person in their 20s,the risk will be much lower than stated. Risks are also based on figures from last summer.

Since then we've had new treatments that reduce risk and new variants that increase it. How do those balance? In short, there are so many uncertainties that this isn't much better than an informed guess on a nice PowerPoint. END

Here's an illustrative graph of the kind of risk distribution you might expect amongst young people. Most people have below average risk, but a few people have a much higher risk, if they have severe respiratory disease, are being treated for cancer, have severe diabetes, etc.

PS: It should be stressed both Covid risk and vaccine risk are v. low for people in their 20s.
However, UK govt is giving slightly mixed message to this group:
"Vaccine risk is almost negligible, so don't worry if you've already had AZ."
"Covid is dangerous, so take a vaccine".

However, graphs published say that the risks are similar, assuming low prevalence, which is currently the case.
Of course, this depends on what you mean by risk (long Covid, ICU, death), but that takes us back to the start: the graphs don't really tell us that much.

Now, if UK were aiming for elimination, getting everyone vaccinated would clearly be huge benefit. That would be my preference.

But UK govt says that is impossible. So what's the strategy? Will people in their 20s need to be re-vaccinated each year? Just old people?