> Manaus shows that pursuing herd immunity through natural infection is not a guarantee.
Not a guarantee of what? Are we suggesting that we have a virus here that, unlike every previous virus, we can only reach herd immunity for with a vaccine?
Not a guarantee of what? Are we suggesting that we have a virus here that, unlike every previous virus, we can only reach herd immunity for with a vaccine?
Have we reached "herd immunity" for syphilis? Herpes? Was smallpox eradicated via "herd immunity" that wasn't reached via a vaccine? Polio?
It is extremely common for viruses to not be eradicated unless there is a vaccine. Even vaccines are not guaranteed to be enough, e.g. with most influenza strains, although flu vaccines have managed to keep the death toll low enough for us to move on with our lives.
Syphilis is a bacterial infection. You can get it more than once. There is no such thing as herd immunity.
> Herpes?
...is transmitted via intimate, direct contact. You don't get herpes by walking into a crowded room, and there's no way to be "immune" to herpes without also being a carrier. Herd immunity isn't a relevant concept.
> Was smallpox eradicated via "herd immunity" that wasn't reached via a vaccine?
Smallpox was eradicated by herd immunity that was achieved via a mixture of natural and vaccine-induced immunity. Initially, a large portion of the population was immune due to natural infection. Over time, vaccinations were targeted to local outbreaks.
> Polio?
We have not eradicated polio. In some (now 3) countries, polio is endemic, and outbreaks are self-regulated by herd immunity.
Herd immunity does not mean that a disease is eliminated. It means that the spread of the disease is naturally controlled.
Not necessarily "naturally".
But yes, my choice of words is confusing there. The point I am making is that herd immunity is not eradication. People (like the OP) confuse the two concepts.
You can have herd immunity in a population, and the pathogen will still circulate. Observing that a virus still infects people is not evidence that herd immunity to that virus has not been achieved.
"Herd immunity" applies to bacterial infections as it does to viral. All it means is that the R-value is low enough that the disease doesn't spread. https://en.wikipedia.org/wiki/Herd_immunity#Theoretical_basi...
As an example, pertussis is a bacterial infection which most US communities have herd immunity to thanks to the pertussis vaccine.
> You can get it more than once.
There are also viral infections you can get more than once. In fact, the South African variant of COVID is likely possible to get even if you've had COVID before.
> Mixture of natural and vaccine-induced immunity.
Sure, just like nearly every virus that has been eliminated via vaccine. As, hopefully, COVID will be. Smallpox was not eradicated without a vaccine.
> We have not eradicated polio
The vast majority of the world has indeed eradicated polio via vaccination, as made clear by the fact that only three countries out of 195 still have a polio problem. The same is true for measles, rubella, and a variety of other diseases, none of which would have been eradicated from most populations without vaccines.
The OP's stance that COVID would be somehow unique amongst viruses or diseases if it needed a vaccine for eradication ignores the history of every disease for which we've mass-vaccinated against in the 20th century, as well as the vast majority of diseases that have not been and never will be eradicated by herd-immunity-reached-through-mass-infection.
It does not apply to Syphilis. Getting an infection today does not prevent me from getting one next month. Even if it did, it doesn't materially affect the rate at which other people get it from me...unless we are rutting like rabbits in some constant random orgy.
Herd immunity was defined by the theory that it would prevent the spread of measles. It only did so with any measurable effect after universal vaccination was introduced.
There is an argument to be made that various strains are different viruses, and that we have herd immunity to some of them. It wouldn't make sense to invent an English name for each one, but that doesn't mean they should be treated as a single thing in all contexts.
And I even stated it as ambiguous depending on how you count strains, I'm not arguing that there is only one way to look at it!
Do you have a specific strain of flu in mind when you claim that we have reached herd immunity "to various strains" without vaccination?
There's also lots of places that don't do much flu vaccination, they don't necessarily have the same strains in circulation forever.
Herd "immunity" was never reached, at least not in the sense that members of the herd with weaker immune systems were protected due to the virus's inability to circulate thanks to widespread, strong immunity. According to this commonly-cited paper [2], nearly all modern cases of "Influenza A" (a specific type of flu) in humans have been from descendants and variants of the original 1918 virus. The variants temporarily disappeared from active circulation in the 1950s when they were initially outcompeted by the then-novel H2N2, but were accidentally leaked from a lab in the 1970s and have circulated in humans ever since. We are still plagued by variants of the 1918 flu today.
The links are in contradiction to each other, the second one kicking off with An estimated one third of the world's population (or ≈500 million persons) were infected and had clinically apparent illnesses (1,2) during the 1918–1919 influenza pandemic. The disease was exceptionally severe. Case-fatality rates were >2.5%, compared to <0.1% in other influenza pandemics (3,4). Total deaths were estimated at ≈50 million (5–7) and were arguably as high as 100 million (7).
I don't really care to argue about it, my initial comment was measured.
The "Spanish" influenza pandemic of 1918–1919, which caused ≈50 million deaths worldwide, remains an ominous warning to public health. Many questions about its origins, its unusual epidemiologic features, and the basis of its pathogenicity remain unanswered.
Which... matches pretty well with the first link. Sure, the outcome of the disease was severe, but we don't know why! And recent studies imply that it was because of sociological phenomena.