Thread by @dvir_a

Estimating real-world COVID-19 vaccine effectiveness in Israel! Now preprint version. TL;DR: Very effective. 66-85% for infection, 87-96% for severe disease.

Below a tweetorial about this new analysis —>


github.com/dviraran/covid…

This started when I tweeted the numbers provided by the ministry of health (MOH) regarding cases of vaccinated individuals. This tweet had more >250K views, so decided it might be better to formulate the analysis and provide full methodology.

https://twitter.com/dvir_a/status/1356503858629984257

Using the daily incidence of cases and daily vaccination counts and developed a formula to quantify the expected number of cases based on those numbers. I then combined it with observed counts provided by the MOH to calculate the effectiveness.

The problem is that those vaccinated (and especially early) have different disease dynamics than the general population. Different demographics and socio-economic levels. How do we correct for that?

Well, instead of correcting, I present the full range of reasonable scenarios and show how they affect the estimation of effectiveness.

For example, for positive cases of 60+, it looks like this. Without correcting (beta=1) we get 83% effectiveness a week after 2nd dose. If that group has half the chance to be positive, it reduces the estimation to 66%. So, we get a lower and upper bound - 66-83% effectiveness.

Note that half chance is very radical, before vaccinations the beta was found 0.75. What is the correct beta, Idk, but it is most probably in this range (0.5-1)

For positive cases <60, it looks like this. Pretty similar (reasonable beta is ~1). Note that in both plots it seems that the 1st dose is not very effective in reducing cases.

Finally, severe/critical/death cases. Chances for severe cases for older population are about 4-fold of the general population (beta=4), and the full reasonable range (beta=2-6) brings us to effectiveness of reducing severe disease by 87-96%.

Caveat here is that severe cases may be delayed and are expected to increase. We will have to see how those numbers change in the coming weeks.

We see that immediately after the 2nd dose the effectiveness jumps. Two options: 1. the 2nd dose is effective immediately. 2. The 1st dose is effective after ~3 weeks. There is some support for the 2nd option. We will have to wait and see numbers from the UK.

All the data used here is publicly available, and I deposited the code and data to recreate the analysis in github.com/dviraran/covid….

I also created an interactive app to allow users to play with the different parameters and see how they affect the estimation of the effectiveness - I also created an interactive app dviraran.shinyapps.io/VaccineEffectI…. Data will be updated once available.

I also want to cite other efforts that took different approaches to show that the vaccine is working by @eran_segal, @ShalitUri, @GazitDoron, and Maccabi.

medrxiv.org/content/10.110…

tinyurl.com/4fmte6d2

medrxiv.org/content/10.110…

In summary, this is the first attempt to estimate the effectiveness of the vaccine in Israel compared to the general population and based on observed counts of cases in vaccinated individuals. The analysis clearly shows that the vaccines are working very well. Go get your shot!