AdvertisementCDC Urges Vaccinated People To Mask Up Indoors In Places With High Virus TransmissionUpdated July 27, 2021Allison AubreyfacebookEmailSubway riders mask up this month in New York City. Wearing masks in all kinds of indoor settings may be the safest way to slow the spread of the delta variant, many health experts say. (AFP via Getty Images)This article was originally published on July 27, 2021.