Fully vaccinated people can still transmit coronavirus, US CDC warns

Fully vaccinated people can still transmit the Covid-19 virus, US Centers for Disease Control and Prevention (CDC) Director Dr Rochelle Walensky said Thursday.

"Our vaccines are working exceptionally well," Walensky told CNN's Wolf Blitzer.

The vaccines work well for Delta in a way to prevent severe illness and death, but "what they can't do anymore is prevent transmission," Walensky said, stressing the need for even vaccinated people to wear masks indoors again.

The Delta variant accounts for an estimated 93.4 per cent of all new Covid-19 cases in the United States during the last two weeks of July, according to figures published by the CDC on Wednesday.

A study released last week by the agency showed the Delta variant produced similar amounts of virus in vaccinated and unvaccinated people if they got infected, suggesting that vaccinated groups who get a breakthrough infection could have a similar tendency to spread the virus as the unvaccinated.