Vaccines do reduce the spread of Covid.
100% prevention is just not in the cards unfortunately. Not without like, 95%+ vaccination rates and stronger vaccines.
But getting vaccinated reduces your chances of contracting a serious case of the disease and it helps you reduce viral load quicker. Both of those things make it less likely you will spread the disease.
Now, vaccinated people can be less risk averse which would of course increase their chances of spreading disease. So there are some competing factors depending on the specific people and their practices.
So when something like a sports league, or a big institution, is designing policies they can't create something that is swiss cheese with all of these different applications based on a million different facts. Like, it's just not sensible and reasonable for them to not have a vaccination policy at all just because Aaron Judge is healthy and in fantastic shape. They have to take the safe course of action. It's reasonable to think that vaccines reduce the spread of the disease for the above reasons. It's reasonable to have policies that require everyone to be vaccinated.
From a policy perspective it's probably not a good idea to approach analysis with anecdotal reasoning. It's not logically sound to try to tear down a sensible policy for a large institution just because you can point to some anecdotes of fully vaccinated people catching Covid or spreading it. You need to approach these things with BROAD first principles. Which are something like:
- Vaccines reduce viral severity
- Vaccines reduce the chance to spread the disease
If your argument against vaccine policies in MLB / Canada starts with "but the vaccine does not prevent Covid" or "but the vaccine does not 100% prevent the transmission of Covid" you're starting from an illegitimate premise.
Even if the policy has the direct effect of say a 20% reduction on transmission within the institution the policy probably makes a lot of sense! good policy