The mRNA COVID-19 vaccines seem to do all of these: they reduce infection; reduce chance of symptoms given infection; and reduces the chance of severe illness g

The mRNA COVID-19 vaccines seem to do all of these: they reduce infection; reduce chance of symptoms given infection; and reduces the chance of severe illness given symptoms. It's much less so for Omicron than for past variants. MMR is similarly effective at infection vs. mumps as the mRNA vaccines are against infection with pre-Omicron SARS-CoV-2. Transmission is a harder question: if you prevent infection in a bunch of people, but also create more asymptomatic people who are likely to go out and about: which effect wins out?