Herd Immunity

[tearstainedbakes]

I think I'm being thick.

Surely herd immunity only happens if we can only get it once.

I thought we already knew that you can get it more than once.

So why are people still talking about hers immunity?

What am I missing?

We don't know how common it is to get it twice.

We're only about 6 months in, and there have been a few cases of known re-infection. There's no way to tell yet if this is because immunity starts to wane generally after 6-8 months or so, or if these cases are outliers. Only time will tell.

If immunity is short lived, then herd immunity is only going to be possible via a vaccine with regular, frequent boosters.

If no vaccine, and immunity is enduring, then it will become a disease of childhood - it'll move through adults, over time and with restrictions to avoid massive peaks, but won't go away and will reappear in waves when enough new people have been born for there to be transmission again (just like pre-vaccine measles outbreaks came around every few years affecting primarily DC plus some adults who has missed it in previous outbreaks)

If no vaccine and short duration immunity, then it becomes an endemic risk (will keep going round like a dangerous cold). Then there will need to be new ways found to live in a world with omnipresent risk of serious illness. Something we may need to be contemplating, perhaps as soon as next year, when we've seen what it is like through the winter virus season and have a better idea of both duration of immunity and progress towards a vaccine.

That's really helpful and interesting, thank you.

If we think how many millions of people have had this. We have heard about a handful of reinfections? So it’s not common at the moment to be reinfected quickly.

I think it will become endemic. There will be some immunity for some people, hopefully a vaccine and better treatment means it’s something we have to live with but doesn’t have such a devastating impact each year.

If there were zero immunity for anyone surely we would be seeing thousands reinfected by now?

Happy to be corrected though.

There are more and more cases of people getting cv twice and have been since July. They are only coming out of countries that got their shit together with testing fairly early on like the States and most of them dont make the medical journals, but if you hang around the COVID support groups on line you'll find them. In the uk where testing wasnt a thing for most in Feb/March/April anyone catching it a second time will be told they couldn't possibly have had it the first.

@tearstainedbakes

I think I'm being thick.

Surely herd immunity only happens if we can only get it once.

I thought we already knew that you can get it more than once.

So why are people still talking about hers immunity?

What am I missing?

Because they're idiots.

@Delatron

If we think how many millions of people have had this. We have heard about a handful of reinfections? So it’s not common at the moment to be reinfected quickly.

I think it will become endemic. There will be some immunity for some people, hopefully a vaccine and better treatment means it’s something we have to live with but doesn’t have such a devastating impact each year.

If there were zero immunity for anyone surely we would be seeing thousands reinfected by now?

Happy to be corrected though.

The small handful of proven reinfections are the tip of the iceberg as most people who've been infected twice won't have managed to get a test the first time, let alone have a sample from then available for genetic testing.

Are we seeing lots (and I’m talking thousands?) of reinfections in countries that did do lots of early testing then?

Sometimes need multiple exposures to get long term immunity or reduced risk of severe illness -- think about needing multiple tetanus jabs in life. I think even Polio isn't actually lifelong immunity.

Good questions, OP. So much not known.

@Delatron

Are we seeing lots (and I’m talking thousands?) of reinfections in countries that did do lots of early testing then?

No, because a reinfection isn't currently considered proven unless the virus was sequenced both times and shown to be significantly different. Even countries that did a lot of testing early on didn't sequence the virus each time plus the countries that got their act together early on either didn't have a massive wave in spring, aren't having a massive wave now or never had a massive problem with the virus at all.

There won't be herd immunity, It will be like other human infections caused by coronaviruses, we will all get it every so often. A vaccine will need to be given every so often to the more vulnerable to it.
We will get new treatments and so as time passes so getting it won't be so risky and life will go on.
For now we are just waiting for medical science to catch up, and whatever is done once we do get to the 'decent treatment its another one of those things' stage which we will eventually even it is 2025/2030 we will look back and say we shouldn't have done it how we did.

Herd immunity without a vaccine would come at high cost in lives

It causes "overshoot" - about 20-25% more people need to have the disease than would be required for herd immunity by vaccine

Adam Kucharski (LSHTM)
threadreaderapp.com/thread/1305436391707467776.html

Some hard hit areas of the world had up to 70% antibodies
UK average is ~8%, nowhere near herd immunity,
even if we assume / hope some additonal % have undetectable immunity

WHO is stating that a herd immunity policy (on wild disease, not vaccine) is a dangerous approach.

Also (from BBC):

The Africa Centres for Disease Control (CDC) has warned that more than 800 million Africans could be infected with coronavirus, if the virus is allowed to spread deliberately with the aim of achieving herd immunity.

The projection is a worst case scenario.

This could put the lives of 8.4 million Africans at risk if immunity was to be achieved naturally, Africa CDC added.

Herd immunity is a situation in which a sufficient proportion of a population is immune to an infectious disease through vaccination and/or prior illness to make its spread from person to person unlikely.

Wessam Mankoula, the incident manager for Covid-19 at the Africa CDC, told the BBC that the risk of deliberately giving the virus an avenue to spread will come at a high human cost.

“In a continent of more than 1.2 billion people, this will mean that we will let the infection get to between 720 – 840 million people to reach this herd immunity,” Dr Mankoula said.

"If we have a vaccine, we will be able to control infections. Without it, this will make our healthcare system vulnerable with a huge number of cases. Our hospitals will also be overwhelmed," he added.

BBC article: Coronavirus: WHO head calls herd immunity approach 'immoral'

www.bbc.co.uk/news/world-54518286