Here's a great retrospective that covers the timeline and the science: https://www.youtube.com/watch?v=JgrMzvasrm8 https://www.youtube.com/watch?v=JgrMzvasrm8

Here's a great retrospective that covers the timeline and the science: https://www.youtube.com/watch?v=JgrMzvasrm8 https://www.youtube.com/watch?v=JgrMzvasrm8 TLDR: We knew the mRNA vaccines were effective at preventing serious disease in late 2020. We didn't know for sure (publicly) if the mRNA vaccines reduced transmission rates until mid 2021, as more research concluded. Mid 2021 is when it was demonstrated that mRNA vaccines reduce transmission of the variants of SARS-CoV-2 at the time. As SARS-CoV-2 continues to mutate, more research needs to be done.