President Joe Biden said Thursday that Covid deaths in the United States will continue to increase due to the spread of the “dangerous” Delta variant, calling it a “serious concern”.

“More than six hundred thousand Americans have died, and with this variation of the Delta, you know there will be others, too. You know it will happen. We need to vaccinate young people,” Biden said at a community center in Raleigh, North Carolina .

The variant, said Biden, is more easily transferable and potentially fatal and “especially dangerous for young people”.

The president warned that Americans who have not yet been vaccinated are particularly at risk.

“The data couldn’t be clearer: if you are vaccinated, you are safe,” said Biden. “You are still at risk of becoming seriously ill or dying if you actually aren’t vaccinated, that’s just a fact.”

According to data from the Centers for Disease Control and Prevention, the delta variant now accounts for at least 20% of all new Covid cases in the USA. The variant has a doubling rate of about two weeks, which puts it on the path to becoming the dominant strain in the U.S. in just a few weeks, said Chief White House medical advisor Dr. Anthony Fauci, on Wednesday.

The authority has described the more easily transferable variant as “questionable variant”.

Experts say the Delta variant could also cause more severe illness in those infected, but more data is needed to be certain.