Are Covid Vaccines “Leaky”?

Question

I've been reading a bit about Marek's disease this weekend. It's an interesting case where the vaccine for Marek's disease has inadvertently allowed highly virulent strains of Marek disease to propagate causing its fatally rate to reach 100% in unvaccinated birds.https://en.wikipedia.org/wiki/Marek%27s_diseaseMy understanding is that COVID vaccines do limit spread, but as can be seen from forums like Reddit's "COVID19 positive" (https://www.reddit.com/r/COVID19positive/) many people who are fully vaccinated do still contract COVID and health officials have stated that it's possible to still spread COVID in these cases.This seems to be a growing issue as more recent variants seem to have adapted to circumvent existing vaccines and we're seeing growing numbers of people now become infected despite being fully vaccinated. Of course, the argument is that if you're fully vaccinated then you're likely to have milder symptoms, but as with the vaccine for Marek's disease we can assume this would then enviably reduce selection pressure against highly virulent strains.I'm really hoping someone can explain to me why this isn't a concern. Admittedly the person who made me aware of this is fairly conspiratorial, but so far I have no good argument against what they're suggesting could happen.

codingdave · Accepted Answer

First, I'd check their source for saying that the number of cases in vaccinated people is growing. I mean, of course it is - 2 is more than 1, so whatever number we are at, it is growing... but is the actual percentage growing? Or is it just the expected rate?
Also, there is little in this world that is black and white. You cannot look at a pandemic and just flip a switch to go from "concerning" to "not a concern". Vaccination is better than not. There really isn't any argument against that. But that doesn't mean we just turned off the pandemic and nobody will ever get sick again. That simply is not how it works.
So could there be long-term consequences? Sure. Does that change what our actions should be today? No.
As far as arguing against such things... don't accept their premises. Check their data sources. Most of the poor arguments out there are based on bad data or myopic logic. Or both.

ksaj · Answer

The only thing I can add to this is that some agencies have at least been clear that even after vaccination, people should still be social distancing and wearing a mask. I realize that is far looser in the US, but here in Canada, it has not been loosened in this way.
With birds, you won't be masking them or keeping them at distances. So their ability to spread disease is significantly higher.
Our take on this up here at least is that you have to do everything to get these numbers down. We recognize that you can still catch and spread the virus even if you've been vaccinated. Apparently you'll get less ill if you are vaccinated and catch it, but you still have to avoid infecting people who have not yet been fully vaccinated - something birds don't have as much control over.