I have a question about COVID spread. Based on what I know of the numbers, the rate of spread + immunity doesn’t add up, but my numbers could be wrong.
It seems to me that one of two things must be true:
Before the vaccine launched, r0 was greater than 1, but still low enough that most people didn’t catch it. Then, after ~50% of people in the developed world got the vaccine (and ~20% of people had already gotten COVID), r0 was low enough that COVID died out in the developed world within a few months.
After the vaccine launched and most people got it, r0 was high enough that COVID continued to spread. Before the vaccine launched, r0 was far higher, and pretty much everyone got it.
But both these things are false. Why?
(One thing that could explain it is that NPIs kept the virus in check, and people started behaving much more riskily after the vaccine became available. This seems intuitively wrong because the vaccine is so much more effective than NPIs but I’m not sure about the numbers.)
(Another possible explanation is that, even though vaccines are 90%(ish) effective at preventing spread, that doesn’t reduce r0 by anywhere close to 90%. Which also seems wrong to me but I don’t know exactly how r0 works.)
I have a question about COVID spread. Based on what I know of the numbers, the rate of spread + immunity doesn’t add up, but my numbers could be wrong.
It seems to me that one of two things must be true:
Before the vaccine launched, r0 was greater than 1, but still low enough that most people didn’t catch it. Then, after ~50% of people in the developed world got the vaccine (and ~20% of people had already gotten COVID), r0 was low enough that COVID died out in the developed world within a few months. After the vaccine launched and most people got it, r0 was high enough that COVID continued to spread. Before the vaccine launched, r0 was far higher, and pretty much everyone got it.
But both these things are false. Why?
(One thing that could explain it is that NPIs kept the virus in check, and people started behaving much more riskily after the vaccine became available. This seems intuitively wrong because the vaccine is so much more effective than NPIs but I’m not sure about the numbers.)
(Another possible explanation is that, even though vaccines are 90%(ish) effective at preventing spread, that doesn’t reduce r0 by anywhere close to 90%. Which also seems wrong to me but I don’t know exactly how r0 works.)