In other words, a so-called "leaky vaccine" or a vaccine that lowers the chances of severe illness, but still allows for transmission of a virus, can create conditions that promote the evolution of more virulent pathogens.
For further reading here is a 2015 NIH-funded study that found "imperfect vaccination can enhance the transmission of highly virulent pathogens.". https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4516275/
The chart entitled "genomic epidemiology of novel coronavirus" shows the increase in mutations after the introduction of these leaky vaccines at the beginning of the year.
Lol what a fool, it's not a mistake they're doing it on purpose.
He's not a fool. He's being careful with his word choices in order for his message to be spread as widely as possible.