Wikipedia:Reference desk/Archives/Science/2021 September 9

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September 9

Covid question

We know that if a vaccinated person catches Covid, the risk of long Covid or complications is much lower compared to if an unvaccinated person catches Covid.

But is catching Covid from a vaccinated person less dangerous than catching Covid from an unvaccinated person?

Logic is the virus would be weakened by the vaccinated person's immune system.

--219.75.107.21 (talk) 09:36, 9 September 2021 (UTC)

The immune system doesn't weaken the virus per se: the virus particle should be exactly the same whether it comes from an unvaccinated person or a vaccinated breakthrough case. Virus particles are made new each time, it's not like they're "worn out" from fighting the vaccinated person's immune system. However, there's evidence that people who've been vaccinated tend to produce less virus and for a shorter period of time, figure 1 of this pdf. I can't find the specific graph I'm thinking of though annoyingly. It shows virus levels produced dropping much faster in vaccinated people on average than unvaccinated. How much this matters depends on the question of exactly how many virus particles are needed to infect someone.

One scenario people worry about with vaccines is Marek's disease, in which it's been suggested that a weak vaccine used on battery chickens has encouraged the evolution of more aggressive virus variants to beat the effect of vaccination. However, it's important to note that i) the vaccine still works very well in stopping the disease, and ii) this is a one-off, there are dozens and dozens of other vaccines which have been used for decades without seeing anything like this kind of effect. Although I haven't found a source specifically pointing to this, my guess is that a major factor there is the tremendously confined nature of battery farming, that squashing huge numbers of chickens together makes it easier for the virus to spread from infected chickens to uninfected ones quickly. Blythwood (talk) 11:03, 9 September 2021 (UTC)

What's a battery chicken? ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:05, 9 September 2021 (UTC)

See Battery cage. --Wrongfilter (talk) 11:23, 9 September 2021 (UTC)

On that point, challenge studies have started in Britain to study questions like this. They seem to be way more altruistic than I to allow a pandemic infection on purpose. Imagine Reason (talk) 20:53, 11 September 2021 (UTC)

Link to uk gov PR. I would imagine that the protocol or/and ethics approval includes some risk assessment, but I could not get my hands on it. (In my opinion, such a document should be public, or at least accessible before registering to be a subject, but I could not find it on the website.)

The argument seems to be that a challenge trial will allow much quicker development of vaccines/treatment and therefore we are in a trolley problem situation, where action might harm a few specific individuals to save many more. I do not really buy it; by the same argument, one could argue to force prison inmates to register for that challenge trial, which would be highly unethical by post-1945 standards. By the way, Human_challenge_study#Ethics is a rather poor section at the moment. Tigraan^{Click here for my talk page ("private" contact)} 09:27, 13 September 2021 (UTC)