Vaccination is neither prevents infection nor spreading. Its about efficiency of the response.
Vaccines frequently prevent infection and spreading. (And yes, they do this by way of priming the immune system.) For example, we eradicated Small Pox with vaccines: https://pubmed.ncbi.nlm.nih.gov/788150/
My understanding is that vaccines do reduce the chance of Covid spreading. But with the Omicron variant, they help a lot with preventing severe illness and only a little bit with helping reduce infectiousness. And Omicron is ridiculously infectious, so it's going to whip right through well-vaccinated areas just like everywhere else.
But in general, reducing the chance that one person infects another is one of the primary purposes of vaccines.
A recent study found that vaccinated people infected with the delta variant are 63 per cent less likely to infect people who are unvaccinated. ...
Others have worked out the full effect. Earlier this year, Ottavia Prunas at Yale University applied two different models to data from Israel, where the Pfizer vaccine was used. Her team’s conclusion was that the overall vaccine effectiveness against transmission was 89 per cent.
Quite. If "Y happens less frequently" then at least one instance of Y has been prevented. But some instances of Y still occur, so "Y can still happen". And if "Y can still happen" then some _clever_ person will say that "aha, Y has not been prevented from happening!"
I _can_ ride a bicycle. So can Mark Cavendish. But these are not equivalents.
None of this is binary, boolean, on-off. Sometimes it seems like this is being deliberately straw-manned with overly simplistic "all or nothing" thinking.
We know that the COVID-19 vaccines prevent a large percentage of infections. We also know that they don't prevent all infections. We know that they are still very worthwhile. We need risk reduction, harm reduction not nit-picky semantic arguments. Medicine is not Boolean logic.