@joeinwynnewood @GreySkies @augieray You might want to look for "COVID neuron fusion"; you might find the university press release uq.edu.au/news/article/2023/06 or the paper, science.org/doi/10.1126/sciadv interesting.

(There is of course nothing to say this is the only mechanism.)

As for vaccination; those figures give the odds of infection on exposure. Where the exposure happens isn't relevant.