Thread by @vipintukur

What would be the future scenario w/ #SARS2 variants?

1. Displacement of Delta by Omicron
2. Long-term co-circulation
3. Omicron wave followed by resurgence of Delta & extinction of Omicron
4-Alternate outbreaks of Omicron & Delta
5-An entirely new VOC may displace the two 1/

We know an Omicron infection protects well against reinfection by Delta in previously vaccinated people, but not so well in those that have not been previously vaccinated. In unvaccinated people an Omicron infection only protects well against Omicron reinfection. 2/

This gives advantage Omicron in a highly vaxxed world. But epidemiology of the two VOC in coming weeks should tell us how efficiently Omicron is displacing Delta 3/

But according to @TWenseleers it's more likely we would see some degree of co-existence & the alternating wave dynamics we see with influenza B. Possibly complemented by additional immune escape variants. 4/

BA.2 might displace BA.1 though, as that would probably represent more subtle antigenic drift - closer to what we see in influenza A/H3N2. 5/

As per @trvrb the more immune escape Omicron has from Delta-specific immunity the more the two variants have distinct ecological niches & so are able to co-exist without stepping on each other's toes 6/

@trvrb also envisages three distinct scenarios 7/

@trvrb “Co-circulation occurs when Ro is similar between Omicron and Delta and/or when there is little cross-immunity, and displacement occurs when there is strong cross-immunity and lopsided Ro”. 8/

If Omicron and Delta co-circulate then annual vaccines would be best formulated as multiple valencies (just like flu vaccine has both B/Victoria and B/Yamagata) and we can expect generally higher levels of viral circulation than in the displacement scenario. 9/

@trvrb believes that we'll see displacement, but we should have first hint at outcome in the next few weeks as we see to what degree the Omicron wave reduces Delta circulation in the US & Europe. 10/

Epidemiologist @adamjkucharski also believes the same. He cites the example of seasonal coronavirus OC43, there's a split into two co-circulating lineages 11/

So, some degree of coexistence & alternating waves with each of the types predominant might be getting more and more likely concludes @TWenseleers 12/