What does a #COVID19 #vaccine with 90% #efficacy imply? It means that 90% of people who are vaccinated will develop sufficient immune response to repel the virus without symptoms (they may or may not still shed #SARSCoV2 and be infectious to some lesser[?] extent) 1/n

How will this help to end the #pandemic? #COVID19 has a R0 of about 3, so #HerdImmunity threshold is about 66% We need to get 66% of the population to an immune state. With 90% #vaccine #efficacy, that implies about 75% of us will need to be vaccinated.

Current surveys indicate #VaccineHesitancy at around 20-40%. If, optimistically, hesitancy is only 20% and we can get 80% vaccinated, then we've hit target. Pessimistically if only 60% are vaccinated at 90% efficacy that's 54% population immunity to #COVID19

54% is still going to leave a lot of people vulnerable, but after #SecondWave we may have 20% of the population with natural immunity. If 20% of the unvaccinated 40% are naturally immune, that another 8% #COVID19 immunity, so the total would be 62% => within touching distance.

So for every % over 90 the true #vaccine #efficacy is, and every % over 60 that we can persuade to get vaccinated, we edge nearer to #HerdImmunity. It also depends on the R0 estimate being under 3 (that's a non-immune pop. without masks or distancing). With #HandsFaceSpace ...

With #HandsFaceSpace Rt (that not R0 from February, but R now) is probably more like 1.5-2 (that's why the #SecondWave has been slower), so it may be possible to stop the #pandemic as long as we stay in #MaskUp mode - without actually reaching true #HerdImmunity.

Would #HerdImmunity mean no more cases? No, it would mean no more self-sustaining large outbreaks. There would still be clusters of #COVID19 cases but they would be self-limiting and not turn into general outbreaks (assuming they don't find some local pocket of low immunity).