This is interesting information.

I did a little deeper digging to see what I could find about vaccines and breakthrough infections. It turns out there are a number of diseases which have breakthrough infections including, but not limited to, COVID-19, influenza, mumps, and chickenpox.

Most recently, a smallpox vaccine has been used to stimulate the immune system to fight monkeypox, which has seen breakthroughs in France.

I wonder whether COVID-19 was the genesis of the change, or simply the final straw.