CNN  — 

With Covid-19 cases rising and the Delta variant gaining increased prevalence in the United States, health experts are reiterating that vaccines are effective in the ways that matter most: preventing severe disease, hospitalization and death.

Speaking to CNN’s Jim Acosta on Saturday, Dr. Anthony Fauci said the vaccines are shown to be “highly effective in preventing symptomatic, clinically apparent disease.”

“When you start seeing what’s called breakthrough infections, if you look carefully at them, the overwhelming majority of those are people who either have no symptoms or only very mild symptoms,” Fauci said. “So the vaccines are still very, very effective in preventing severe disease.”

The Delta variant has “pretty much taken over” in the US, said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital in Philadelphia and a member of the US Food and Drug Administration’s vaccine advisory committee. But it’s clear the vaccines work against the Delta variant, too, he said.

“Despite the rise of the Delta variant, still 97% of people who are hospitalized or killed by this virus are unvaccinated,” Offit said. “If the Delta variant were escaping, essentially, immunity induced by vaccination, then you should have seen a rise in people who are vaccinated, but nonetheless were still hospitalized and killed. And that hasn’t happened.”

Yet the pace of inoculations is slowing, with less than half of the US population – 48.5%, per the latest data from the US Centers for Disease Control and Prevention – fully vaccinated. And it’s the communities with lower vaccination rates that are at risk.

Among those states that have fully vaccinated less than half of their residents, the average Covid-19 case rate was 11 new cases per 100,000 people last week, compared to 4 per 100,000 among states that have fully vaccinated more than half of their residents, according to a CNN analysis o