Fully vaccinated people who get a Covid-19 breakthrough infection can transmit the virus, US Centers for Disease Control and Prevention Director Dr Rochelle Walensky said yesterday according to CNN.

"Our vaccines are working exceptionally well," Walensky told CNN's Wolf Blitzer. "They continue to work well for Delta, with regard to severe illness and death -- they prevent it. But what they can't do anymore is prevent transmission."

That's why the CDC changed its guidance last week and is now recommending even vaccinated people wear masks indoors again, Walensky said.

Last week, the agency released a study that showed the Delta variant produced similar amounts of virus in vaccinated and unvaccinated people if they got infected -- data that suggests vaccinated people who get a breakthrough infection could have a similar tendency to spread the virus as the unvaccinated, reports CNN.