You're correct that it's possible for vaccines to be distributed in a way that promotes mutations[1]. You're also correct that there are many factors, including

You're correct that it's possible for vaccines to be distributed in a way that promotes mutations[1]. You're also correct that there are many factors, including number of times the virus replicates and also selective pressure. At this point, it looks like our mRNA vaccines: - leave a short enough window between doses to minimize mutations - reduce viral load within a vaccinated person[2] - prevent many transmissions entirely[3][4][5] ...which, added all up, appears to net out the way you'd expect: the vaccine reduces the risk of mutations. 1. https://www.npr.org/sections/health-shots/2021/02/10/965940914/covid-19-vaccines-could-add-fuel-to-evolution-of-more-coronavirus-mutations https://www.npr.org/sections/health-shots/2021/02/10/9659409... 2. https://www.nature.com/articles/s41591-021-01316-7 https://www.nature.com/articles/s41591-021-01316-7 3. https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/fully-vaccinated-people.html https://www.cdc.gov/coronavirus/2019-ncov/science/science-br... 4. https://www.physiciansweekly.com/covid-19-breakthrough-infections-involve-lower-viral-load-following-mrna-vaccination/ https://www.physiciansweekly.com/covid-19-breakthrough-infec... 5. https://www.scientificamerican.com/article/the-crucial-vaccine-benefit-were-not-talking-about-enough1/ https://www.scientificamerican.com/article/the-crucial-vacci...