Question: With WHO recommending that vaccinated people continue to wear masks and the Delta variant spreading, should I resume mask wearing?

Answer: It depends.  In good news, yesterday Moderna announced results of a lab-based study, which showed that the Moderna vaccine is highly likely to be effective against variants of concern, including Delta; we already have solid data that full vaccination with Pfizer and AstraZeneca is effective against the Delta variant; and we know that masking is highly protective.  In bad news, the Delta variant is far more transmissible than even the Alpha variant; no vaccine is 100% effective; and there are still portions of the country (let alone the world) where large swaths of the population are unvaccinated.  If you are in an area with low vaccination coverage, an area with ongoing community transmission, or with a group of people you know are unvaccinated, then I would suggest wearing a mask when you are in a situation that increases your exposure risk (e.g. close-contact setting, crowded places, closed spaces).  A lot of “ifs” there, I realize, but such is the way of an “it depends” answer.  As for me, I bring a mask with me everywhere and don it occasionally, depending on the situation.