How different masks protect against Covid-19, and its delta and lambda variants

Masks help prevent the spread of infection, both with the original Covid-19 virus, and the delta variant that is taking hold of the US, and other variants like the lambda variant and those that will inevitably arise. While mask mandates were lifted in some locations of the country months ago, the US Centers for Disease Control and Prevention (CDC) recently reversed its masking recommendations even for the vaccinated. Its mask guidelines now recommend that people in areas with high transmission wear masks indoors while in public.