Not impossible, just can't be done by vaccination alone. The remaining required percentage of the population would have to get immunity from getting sick.
This is what I was getting at in the grandparent post. 50% -> 60% and 85% -> 95% might both seem like they protect 10% more of the population, but the qualitative effect on the spread of the pandemic and be quite different. 60% might be enough to get herd immunity (with masks and social distancing), while 50% is not. Both 85% and 95% are definitely enough to get herd immunity, so to some extent that added protection matters less.
It's still not any kind of "inflection point". The difference between 0 and 5% is an even sharper slope-- from infinity to 1200% of the population ;)
Also-- all we know about is effects on symptomatic illness and we can't be sure there's any large transmission benefit (and if there is, it's probably smaller than the efficacy against symptomatic illness).
If the virus is still circulating in volume, the difference between a 95% effective vaccine and a 70% vaccine is a further 6x reduction in risk for the individuals that have it. Every little bit helps, but a really high efficacy is very nice to have.
garmaine|5 years ago
This is what I was getting at in the grandparent post. 50% -> 60% and 85% -> 95% might both seem like they protect 10% more of the population, but the qualitative effect on the spread of the pandemic and be quite different. 60% might be enough to get herd immunity (with masks and social distancing), while 50% is not. Both 85% and 95% are definitely enough to get herd immunity, so to some extent that added protection matters less.
mlyle|5 years ago
Also-- all we know about is effects on symptomatic illness and we can't be sure there's any large transmission benefit (and if there is, it's probably smaller than the efficacy against symptomatic illness).
If the virus is still circulating in volume, the difference between a 95% effective vaccine and a 70% vaccine is a further 6x reduction in risk for the individuals that have it. Every little bit helps, but a really high efficacy is very nice to have.