On Thu, 9 Apr 2020 19:56:00 +0100, The Natural Philosopher wrote:

I think you dont get proper herd immunity until the infection rate drops
to zero ...

Mean, over a population, infection rate of less than one from someone
infected. Obviously the lower the infection rate the faster it dies
out.

... which means that the chances of someone with it meeting someone
who has never been exposed are essentially nil. THAT takes a hell of a
lot of people getting it.

It's reckoned that SARS-CoV-2 needs to infect 60 to 80% of the
population for "herd immunity" to start having an effect. There is a
mathematical relationship between the natural infection rate and the
percentage of population that needs to be infected for the herd
effect to start having an influence.

The problem is that many have it and hardly feel it.

Well quite, I had a "funny throat" about the start of lockdown. Felt
a bit "lumpy" but not sore or tickly, little bit of a cough.
Obviously something but what? I doubt it was Covid-19.

Until there is a decent anti-body test available and significant
numbers of people are tested we don't really know how widespread
SARS-CoV-2 actually is.

All we can do is watch the hospital admissions and once they are
showing a consistent fall for a couple of weeks, lift some of the
more draconion ones and keep a close eye on the admissions. If they
start to exponentialy rise bang the restrictions back on. The tricky
bit is spotting early enough the difference between the rise that
will occur when the restrictions are lifted and a rise that means
it's starting to take off again.

--
Cheers
Dave.