Many scientists are reluctant to say with certainty that the vaccines prevent transmission of the virus from one person to another. This can be misinterpreted as an admission that the vaccines do not work. That’s not the case. The limited data available suggests the vaccines will at least partly reduce transmission, and the studies to determine this with more clarity are underway. There should be more data within the next couple of months. Until then, precautionary measures like masking and distancing in the presence of unvaccinated people will remain important. It is true that, according to the clinical trial data, both the Pfizer-BioNTech and Moderna vaccines are highly effective at preventing COVID-19, the disease, but it’s unknown how well they prevent infection with SARSCoV 2, the virus. Although COVID-19 and SARS-CoV-2 are often used interchangeably, they are fundamentally different. You can’t have the disease without the virus, but you can have the virus without the disease — as many asymptomatic people already know. It’s possible that vaccinated people are protected against COVID-19 themselves, but still spread SARS-CoV-2 to others who are not vaccinated.