Fully vaccinated people who get a Covid-19 "breakthrough" infection can spread the virus to others even if they are not symptomatic, Centers for Disease Control Director Rochelle Walensky told CNN on Thursday.
She warned that an autumn/winter surge in the Covid "Delta" variant could again see hundreds of thousands of cases per day.
"Our vaccines are working exceptionally well," she said. "They continue to work well with delta with regard to severe illness and death, but what they can't do anymore is prevent transmission."
