Thread by @vipintukur

Transmission of SARS2 #Omicron’s subvariants BA.1 & BA.2

A Danish households transmission study

➡️ The secondary attack rate was estimated as 29% and 39% in households infected with Omicron BA.1 and BA.2, respectively. 1/

➡️ BA.2 was associated with an increased susceptibility of infection compared to BA.1.

-Unvaccinated (Odds Ratio (OR) 2.19; 95%-CI 1.58-3.04),
-Fully vaccinated (OR 2.45; 95%-CI 1.77-3.40)
-Booster-vaccinated (OR 2.99; 95%-CI 2.11-4.24). 2/

➡️ There was an increased transmissibility from unvaccinated primary cases in BA.2 households when compared to BA.1 households, with an OR of 2.62 (95%-CI 1.96-3.52). 3/

➡️ The pattern of increased transmissibility in BA.2 households was not observed for fully vaccinated & booster-vaccinated primary cases, where the OR of transmission was below 1 for BA.2 compared to BA.1. 4/

➡️ Key Takeaways:

1-Omicron BA.2 is inherently substantially more transmissible than BA.1,

2-It also possesses immune-evasive properties that further reduce the protective effect of vaccination against infection. 5/

3-However, it doesn’t increase its transmissibility from vaccinated individuals with breakthrough infections. 6/

medrxiv.org/content/10.110…

Although vaccinations, in particular booster vaccinations, did protect ag infection, the 2.45 (fully vaxxed) & 2.99 (boosted) fold higher odds of infection in BA.2 households indicate that BA.2 as a phenotype represents a further step in immune evasion in the Omicron lineage. 7/

However, it is likely that this change came w/ an evolutionary cost for BA.2
The combination of high incidence of a relative innocuous subvariant has raised optimism.
Important to follow the future evolution of BA.2 closely, as well as future emergent subvariants. 8/