2/ First, we make estimates using a combination of the COVID spike Ab & nucleocapsid Ab to determine what proportion of our population is protected at a given time.
ie, either previous infection (nucleocapsid) or vaccination (spike Ab) or combined Infection & vaccination.
3/ But if there was 95% immunity in 2021, how did #Omicron go bonkers infecting so many in 2022?
The infection rates reflect #Evolution. The I ntense contagiousness of this variant & enhanced immune escape mutations plus waning protection from previous vaccination & infection.