evidence: Vaccinated People With Breakthrough Infections Can Spread The Delta Variant, CDC Says [...] The CDC said the finding that fully vaccinated people could spread the virus was behind its move to change its mask guidance. [...] "This finding is concerning and was a pivotal discovery leading to CDC's updated mask recommendation. The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones," Walensky said.