Thread by @ariehkovler

Israel's Channel 12 reported the Israeli Health Ministry's initial assessment of Omicron based on data given to them by the South African health authorities. This data is at best preliminary and I have a lot of questions. Sharing with appropriate caveats:

Per this report, 3 vax doses (2+booster) provide:
* 90% protection against Omicron infection vs 95% effectiveness against Delta
* Similar level of protection against severe disease in Omicron and Delta

THIS IS VERY PRELIMINARY DATA -- DON'T BE SURPRISED IF IT CHANGES

Per this report, unvaxxed people who have recovered from past infection with another Covid variant are *double* as likely to catch Omicron as they were to catch Delta.

THIS IS VERY PRELIMINARY DATA -- DON'T BE SURPRISED IF IT CHANGES

If the data on double the reinfection rate is accurate, it might help explain what we're seeing in South Africa where so much of the population's immunity was from past infection.

Per the report, the really bad news is Omicron appears to have an R that's 1.3x that of Delta. That's a crazy high infection rate. Means case numbers can spiral out of control almost before you notice them.

THIS IS VERY PRELIMINARY DATA -- DON'T BE SURPRISED IF IT CHANGES

I have questions about this data, not least how there can possibly be vaccine effectiveness data for people who've had booster doses, when basically nobody in South Africa has had a booster dose. So take it all with a handful of salt for now.

Another point is that vaccine effectiveness is compared to the unvaccinated. So even if vaccine effectiveness was unchanged and Omicron was more infectious, then everyone, vaxxed and unvaxxed, would have a higher chance of caching it than Delta.

I presented the numbers in this thread as they were presented on the news. But their presentation was misleading.

A 95%->90% drop in vaccine effectiveness translates to "double as likely to get Omicron compared to Delta".