The United States will not lock down again to curb Covid-19 but "things are going to get worse" as the Delta variant fuels a surge in cases, mostly among the unvaccinated, top US infectious disease expert Dr Anthony Fauci said on Sunday.

A sufficient percentage of Americans have now been vaccinated to avoid lockdowns, Fauci said on ABC's "This Week".

"Not enough to crush the outbreak, but I believe enough to not allow us to get into the situation we were in last winter," he said.

The average number of...