Thread by @dgurdasani1

Wanted to say - although the Imperial paper shows protection from hospitalisation *if infected* remains comparable between omicron and delta, the protection *from infection* is vastly reduced. This will mean overall reduction in efficacy against hosp with omicron.🧵

To explain further - vaccine efficacy against hospitalisation is two components:
- protection against infection
-protection against hospitalisation *if infected*

The Imperial study suggests that while the latter isn't affected much (70-80% protection with 2 doses, boosters) *if infected*, your protection from infection is really reduced with omicron. This means *overall* protection from hosp is lower.

Omicron is able to go where delta wasn't able to efficiently- it's able to infect vaccinated people, people with prior infection more efficiently than delta due to escape. While protection from severe disease *if infected* still holds, relative chance of infection is higher.

As @_nickdavies points out here, this is worrying -it means it can infiltrate part of the wall we've created with vaccines particularly for vulnerable groups- the growth we're seeing is because it's ability to escape prior immunity more compared to delta.

https://twitter.com/_nickdavies/status/1473941671196905478?t=xz4JQRSCntUagT_ehYEyWg&s=08

Omicron infections will be disproportionately higher *relative to delta* in those who are boosted/vaccinated/and previously infected. While protection against hosp with vaccines if infected holds, these groups are now more likely to be infected, so overall protection still lower.

Small reductions in protection against severe disease (protection from infection and then hosp) can translate to large differences at population level - especially in vulnerable groups where vaccines will now provide overall lower protection.

So, multilayered mitigations, and limiting socialisation over Christmas is still vitally important.

https://twitter.com/_nickdavies/status/1473941693988753410?s=20

The 'mild narratives' don't really reflect the real complexity of how omicron is spreading - the very different profile of spread needs to be considered to understand full impact, and the rate of spread. And escape, a major advantage of omicron is a key problem here.