This is clearly false, or spread in general would be much lower.
It's not a single event, it's an event at every contact, every day/hour, repeated, again and again and again. Your chance is dramatically higher than you think. From a mathematics stand point, I think this is more like the "same birthday day/month" problem. Where if you have 23 random people in a room, there is a greater than 50% chance 2 of them will have the same birthday day/month. Not that you specifically will have the same, but that two of them will. Now, with COVID, you repeat that experiment again and again and again. Eventually, you will be the one. Maybe not the first 100 times, but keep doing it and eventually it'll be you. Bonus, with COVID being the one just once may be enough for lasting impacts.
Reducing spread is the best reduction to that chance.
It's a group project. Always has been. Trying to pretend otherwise doesn't change that. It's a public health problem and needs a public health solution. Which, by definition, is a group, the public.
There will be some that hold out. We don't need 100% anyway. There's always that slacker on the team and group projects can still work out. The trick is always that the number of slackers needs to be low enough. We've covered all the ways to encourage and slowly exclude from society (hence remove from the public group) unvaccinated people. There's some that will go that route, but it's way less than you think. Bonus, why should they get to dictate the impact to everyone else? Nobody likes the slacker on a group project that lets the rest of the team do all the work and gets to coast along.
Except it still doesn't work that way, and never has. While a vaccine helps train your immune system to fight off infection and give you a huge head start and advantage, it has always worked best because of the group impact of everyone being vaccinated keeping spread low so that your personal immune system rarely has to do anything.
Every replication is a chance for a mutation. The vast number of mutations happen in the unvaccinated, or people where the vaccine didn't work.
For each mutation, that new version is either able to replicate and spread better, the same, or worse than the prior one.
So, there is some pressure where mutations that are better able to breakthrough vaccine protection will be able to spread while mutations that are the same or worse will not be able to spread. To really be an issue, it needs to not just be able to infect a vaccinated person, but also replicate in them and be able to spread on to others better than other variations are spreading.
It's not a directed change, just trial and error. Seeded from large replication trying to spread and either failing or succeeding. So, the larger the uncontrolled spread, the more replication and mutations and attempts at spread are occurring.
It's much faster and more direct with antibiotic resistant bacteria. The bacteria replicates and the antibiotic kills off most of them. The surviving bacteria replicates. The antibiotic kills off most of them again, repeat. Eventually, the only bacteria surviving are the mutations that were able to survive and they go on to spread to the next person.
