Studies suggest that with regard to the original Covid-19 strain and Alpha ("UK" strain, the mRNA vaccines are 90% effective at preventing any infection, including asymptomatic infection. https://www.cdc.gov/media/releases/2021/p0607-mrna-reduce-risks.html This means that if 100 unvaccinated people are infected with Covid, you would predict 10 equally-exposed vaccinated people would be infected with Covid (a tenfold reduction in relative risk of any infection, including asymptomatic in