Thread by @chrischirp

THREAD on all the reasons why I think Omicron does *not* signal the end of the pandemic

TLDR: vaccines & mitigations can hasten its end but we're not done yet & Omicron is just another milepost on the road.

So here goes: Omicron is the 4th major variant to dominate here 1/10

But variants aren't single blocks either - Delta in the UK ended up being mostly subtype AY.4 and AY.4.2 was taking over when Omicron came - and now BA.2 is taking over from BA.1.1. which took over from BA.1. 2/10

Covid evolves rapidly, but this isn't straightforward.

None of the main variants evolved *from* each other - instead so far they are all distinct, becoming gradually fitter via subvariants until replaced by an entirely new variant. 3/10

H/T

The further away a variant is from wild type, the lower vaccine protection against infection.

The further away a variant is from that which previously infected you, the more likely you are to be reinfected. 4/10

It is also not true that variants are becoming milder.

Delta was *more severe* than Alpha which was *more severe* than original covid.

Omicron *is* milder than Delta but likely not milder than original covid... and it's not part of a steady progression to mildness. 5/10

Because almost all Covid transmission happens while people have no or few symptoms, there is no particular reason for severity to play a role in evolutionary selection.

NERVTAG thinks Omicron's mildness likely pure chance & next one is likely to be more severe again. 6/10

Meanwhile, vaccines are really good but even booster shots have waning efficacy against Omicron and further vaccine doses likely have diminishing returns.

Esp as covid evolves further away from wild type which current vaccines are based on. 7/10

It's also too soon to say Covid is endemic. Endemic means that the disease is in some ways stable or predictable (but not nec mild!)

World has just seen steepest ever exponential surge. Who predicted this in November?

Covid may well become endemic but it's not there yet. 8/10

We just *don't know* how coronaviruses evolve in the long term in humans, or over what timescales.

We also don't know what will happen over coming years as the virus jumps into animals and back into humans again. 9/10

Finally, we've called pandemic over after *every* wave.

Omicron is just the latest wave for which we are doing this.

No particular reason to think it's true this time (tho' we *are* closer to end).

We *can* hasten pandemic end through vax + public health mitigations. 10/10