Infection rates-herd immunity?

[Desperado40]

This is a question to someone more knowledgable than me. I keep thinking, with the high infection rates, so many hunderds of thousands of people have already had coronavirus. Should this not help to achieve some sort of herd immunity to the virus? I know that we are putting high hopes for the vaccines, but should this not help somewhat as well?

Having the virus once doesn't seem to give lasting immunity, many have already got ill the second time.

Vaccines give a much stronger immunity, that's why herd immunity through vaccination is the way out.

OP - re "with the high infection rates, so many hunderds of thousands of people have already had coronavirus. Should this not help to achieve some sort of herd immunity to the virus?"

It's not enough. Smallpox was around for thousands of years without ever reaching herd immunity before it was eradicated with a mandatory vaccination program.

You need tens of millions to have been infected before the infection rate will noticeably slow even without infection

"Having the virus once doesn't seem to give lasting immunity, many have already got ill the second time"

Many people I know who have had COVID-19 in March still have high levels of antibodies. In fact, there are very few documented cases of reinfection among more than 80 million cases around the world.

Recent studies such as this one and one [[https://www.eurekalert.org/pub_releases/2020-12/mu-cil122020.php]] have shown persisting immunity.

Sorry about the failed links. This is what I meant to say:

Recent studies such as this one and this one have shown persisting immunity.

Myself and ds1 have just finished our second bout with cv (first was end March) so any sort of herd immunity will only work for a few months on a rolling basis. Helpful but not a solution in itself.

In countries (US, Brazil) where the virus has just been left to spread since May there is no sign of any useful level of herd immunity as yet (I'm sure it would come in time, akthoughbwith a very high body count).

Seeing as we have a vaccine now, with likely more to follow, it seems sensible to me to try and keep a lid on it for another few months whilst we roll it out.

@CoteDAzur

I agree

It does not appear to be a good idea at the moment to go for herd immunity as a strategy

However, the studies you quote should not be disregarded and research on natural acquired immunity post infection should continue.

I do not think that those who have already had Covid should be pushed to get vaccinated until more information is available

I still don't know how the vaccine confers immunity but wild infection cannot do that. I mean, I get that vaccine is safer way to get immunity, but MNers constantly say that wild infection won't give any immunity.

The high number of infections together with the roll out of the vaccine programme should help us reach herd immunity more quickly. However, as others have said that doesn't mean it's a strategy, just a result of the rapid spread of the new strain.

sorry variant

If human immunity from the virus was persistent and no new humans were ever added to the pool then once around 40 or 50 million of us had had the virus it v would find it increasingly difficult to propagate

The herd immunity threshold increases with the transmissibility of a disease ie the easier it is to catch, the more people need to be immune for herd immunity to prevent transmission.

Herd immunity threshold = 1 - 1/R0

where R0 is the basic reproductive number, the number of people each infectious individual infects on average in a homogenous, static population where no one has immunity. That's not the same as the R number being talked about now, which is the effective reproductive number ie the average number of people currently infected by each infectious individual now that some people have immunity and with the current interventions eg lockdowns.

The more transmissible the virus, the more people each infectious person infects ie R0 is higher and the herd immunity threshold increases.

Say R0 for COVID 19 is 3.5, the herd immunity threshold is 71%

If R0 for the new variant is 4.5, the herd immunity threshold is 78%

Wild infection can do it ragged - eventually and at great cost (human and financial). Just not anytime soon. I think what we'll see here and countries like France, the US etc is a combination of vaccination and infection acquired immunity ending things. In other countries - Norway, New Zealand, China, it will be end by vaccination. And in the poorest, the infection will run its course.

Thanks for the posts, interesting links and info.

@trulydelicious - Re "It does not appear to be a good idea at the moment to go for herd immunity as a strategy"

It is a very bad idea.

"Herd immunity" is a term used almost entirely in the context of vaccination for human populations. and that is because 9 times out of 10 wild infection just won't reach it.

Chicken pox, rubella, and measles have been around for thousands of years with their pathogens hardly mutated. Before widespread vaccination programs, herd immunity was still nowhere in sight. Smallpox was only eradicated with mandatory vaccination, not waiting for herd immunity.