>the risk of developing symptomatic COVID-19 was 27 times higher among the vaccinated, and the risk of hospitalization eight times higher
The denominator in those odds ratios seem to fishy to me. Comparing people who were previously infected with COVID and vaccine recipients does some weird conditioning on getting COVID, so it should hide risks of developing symptomatic COVID and hospitalization for people who got COVID previously. It seems to me that the risks should be "cumulative" for people who were previously infected (i.e., the denominator should include symptomatic infections and hospitalizations for previous COVID variants and not just delta) rather than "zeroing" those risks for this group and just focus on delta re-infection. The decision to only focus on delta infections will bias up the OR estimates for vaccine (in)effectiveness, so we should read the results of this paper as the possible upper bound of the ORs.
Also, the study compares the risk of delta infection, meaning that people cannot really just say "I won't get vaccinated because natural immunity is better" as the variants that provided that natural immunity are not "dominant" anymore, meaning that the opportunity to acquire natural immunity against delta is probably close to zero at this time.
Also also, isn't it something that is known that natural immunity is better than vaccine-acquired immunity? The trade-off is that natural immunity has the "side effect" of actually having to fight off and survive the illness?
You raise a good point that it would be useful to report the "cumulative" risk for people previously infected.
However the goal of this research is specifically evaluating risk of reinfection, not the cumulative risk of SARS-COV-2 infection. The fact is that a vast majority of people survive initial SARS-COV-2 infection, so the pure risks associated with reinfection are also equally useful to know.
The decision to focus on delta infections does impact the OR estimates for vaccine effectiveness as you mention. But again this was one of the primary research goals of the paper - to evaluate the risk of reinfection by comparing natural immunity to vaccine-induced immunity in the context of a variant with mutations conferring immune escape.
> the variants that provided that natural immunity are not "dominant" anymore
This was controlled for in the study by censoring data based on the date of previous infection.
> The trade-off is that natural immunity has the "side effect" of actually having to fight off and survive the illness?
Yes, and people need to stop interpreting the title and cited paper as a manifesto against vaccination. Rather, the study provides valuable data on the efficacy of natural and vaccine induced immunity in the context of evolving variants, which will be useful in guiding public health policy and also formulating next generation vaccines that improve upon the current formulations.
> Also also, isn't it something that is known that natural immunity is better than vaccine-acquired immunity?
Yes, I pointed this out elsewhere in the thread, but it has somehow been verboten until very recently to state it in regards to Covid. My brother-in-law was even told by the people administering his vaccine that having had a prior Covid case put him at more risk and made it even more essential that he get vaccinated.
It does not seem unreasonable to me to extrapolate that people who caught COVID-19 once are more likely, as a group, to be exposed to it again in the future. That would be a matter of their environment rather than their individual resistance to the virus. I haven't seen any studies on that issue, though.
In any case the vaccine is safe, effective, and way better than actually catching COVID-19. And in the event that you did already recover from COVID-19, getting the vaccine doesn't hurt and will boost your immunity even further. So—unless you have a specific medical condition which dramatically increases your changes of an adverse reaction–you should just get the vaccine.
The denominator in those odds ratios seem to fishy to me. Comparing people who were previously infected with COVID and vaccine recipients does some weird conditioning on getting COVID, so it should hide risks of developing symptomatic COVID and hospitalization for people who got COVID previously. It seems to me that the risks should be "cumulative" for people who were previously infected (i.e., the denominator should include symptomatic infections and hospitalizations for previous COVID variants and not just delta) rather than "zeroing" those risks for this group and just focus on delta re-infection. The decision to only focus on delta infections will bias up the OR estimates for vaccine (in)effectiveness, so we should read the results of this paper as the possible upper bound of the ORs.
Also, the study compares the risk of delta infection, meaning that people cannot really just say "I won't get vaccinated because natural immunity is better" as the variants that provided that natural immunity are not "dominant" anymore, meaning that the opportunity to acquire natural immunity against delta is probably close to zero at this time.
Also also, isn't it something that is known that natural immunity is better than vaccine-acquired immunity? The trade-off is that natural immunity has the "side effect" of actually having to fight off and survive the illness?