[AndrewBissell]

> The good news is that viruses tend to get less dangerous over time.

One notable exception was Marek's disease in chickens, where the widespread administration of leaky vaccines (which suppressed symptoms and complications but not transmission) led to the breeding of hotter and hotter strains in the vaccinated flocks, which became more lethal to unvaccinated chickens.

[timr]

That's a particularly fearful take on this article, which did not show that vaccines "led to the breeding of hotter and hotter strains":

https://journals.plos.org/plosbiology/article?id=10.1371/jou...

What it showed is that when you take a group of chickens, infect them with multiple strains of different virulence at the same time, and partially protect all of them with a vaccine, the ones with the most severe infection live longer, which allows them to spread more of the most severe virus than they would otherwise.

Said differently: if you don't let the "bad" virus kill the hosts, it can spread more.

Well, sure.

[AndrewBissell]

"In recent years, experts have wondered if leaky vaccines were to blame for the emergence of these hot strains. The 1970s introduction of the Marek’s disease immunizations for baby chicks kept the poultry industry from collapse, but people soon learned that vaccinated birds were catching 'the bug' without subsequently dying. Then, over the last half century, symptoms for Marek’s worsened. Paralysis was more permanent; brains more quickly turned to mush.

'People suspected the vaccine, but the problem was that it was never shown before experimentally,' said virologist Klaus Osterrieder of the Free University of Berlin, who wasn’t involved in the study. 'The field has talked about these types of experiments for a very long time, and I’m really glad to see the work finally done.' "

https://www.pbs.org/newshour/science/tthis-chicken-vaccine-m...

Not trying to raise alarm here or say that this necessarily will happen with SARS-CoV-2, there are tons of big differences. In general, we should expect it to become less lethal over time, but the vaccines may have introduced a confounding factor to the usual selection for milder disease.

[timr]

> Then, over the last half century, symptoms for Marek’s worsened. Paralysis was more permanent; brains more quickly turned to mush.

Sigh. Could the author choose more inflammatory language?

This is half of the problem with Covid-related reporting today: hack journalists who simply cannot resist using horror-movie language to describe illness.

> Not trying to raise alarm here or say that this necessarily will happen with SARS-CoV-2, there are tons of big differences. In general, we should expect it to become less lethal over time, but the vaccines may have introduced a confounding factor to the usual selection for milder disease.

As I said, I think that's an over-statement, having read the original paper. But sure, theoretically, if you have a vaccine that only partially protects against some really severe strain, that strain could escape and go on to become more severe over time.

I'm not sure what we're supposed to do with this information. Not vaccinate? Stay inside forever and suck our thumbs?

In chickens, we probably don't care enough to invest a ton of money into in creating a new vaccine every year. In humans, that's not a problem. If a more virulent form of SARS comes along that escapes the vaccines, we'll make a new vaccine. We're getting pretty good at it now!

(I realize you're not on this side of the argument. I'm just reacting generally.)

[quotemstr]

> I'm not sure what we're supposed to do with this information. Not vaccinate? Stay inside forever and suck our thumbs?

Switch from vaccinating everyone to vaccinating the most vulnerable and using antivirals to treat the illness when it's severe.

> If a more virulent form of SARS comes along that escapes the vaccines, we'll make a new vaccine. We're getting pretty good at it now!

And what if we can't one year --- for any reason? Then billions of people have their brains turn to mush. I don't want human survival to depend on an annual drug refresh.

[AndrewBissell]

> I'm not sure what we're supposed to do with this information. Not vaccinate?

If the actual progression of Covid shows something like it is happening I would say that would be called for for everyone except the high-risk groups, yes.