Fauci, the nation's top infectious disease expert, also said he doesn't foresee additional lockdowns in the U.S.

because he believes enough people are vaccinated to avoid a recurrence of last winter.

Fauci's warning comes days after the Centers for Disease Control and Prevention changed course to recommend that even vaccinated people return to wearing masks indoors in parts of the U.S.

where the delta variant is fueling infection surges.

"So we're looking, not, I believe, to lockdown, but we're looking to some pain and suffering in the future because we're seeing the cases go up, which is the reason why we keep saying over and over again, the solution to this is get vaccinated and this would not be happening," Fauci said on ABC's "This Week.".

According to data through July 30 from Johns Hopkins University, the seven-day rolling average for daily new cases in the U.S.

However, people are "getting the message" and more are rolling up their sleeves amid the threat of the delta variant, according to the director of the National Institutes of Health

Francis Collins said on CNN's "State of the Union" that vaccinations are up 56% in the U.S

Louisiana, which has the most new cases per capita among states in the past 14 days, has seen vaccinations up threefold over that period, Collins said

"That's what desperately needs to happen if we are going to get this Delta variant put back in its place, because right now it's having a pretty big party in the middle of the country," Collins said

Collins also said that even with the prevalence of the Delta variant, the shots are working "extremely well" and reduce a person's risk of serious illness and hospitalization "25-fold." The guidance for vaccinated people to start wearing masks indoors again in certain places with worsening outbreaks, he said, is mostly meant to protect unvaccinated and immunocompromised people

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