As of Tuesday night, 663,913 people in the US have died of Covid-19, according to Johns Hopkins University data. According to the US Census Bureau, the US population as of April 2020 was 331.4 million.

It's a sobering toll that comes as hospitals in the US are struggling to keep up with the volume of patients and more children are grappling with the virus. In hopes of managing the spread and preventing more unnecessary deaths, officials are implementing mandates for vaccinations in workplaces and masking in schools.

They're fighting against daily case, hospitalization and death rates that jumped after the early summer as the highly contagious Delta variant became dominant.

The country averaged more than 152,300 new Covid-19 cases each day over the past week as of Tuesday -- more than 13 times than what it was on June 22, when the average was at its lowest of 2021 (11,303 daily), according to Johns Hopkins University data.

The US averaged 1,805 new Covid-19 deaths each day over a week as of Tuesday -- significantly higher than the low average of the year (218) reached July 5, according to Johns Hopkins.

With only 54% of the population fully vaccinated, the rate of people initiating vaccinations each day (more than 341,900) is a 4% drop from last week and 28% drop from a month earlier, according to Centers for Disease Control and Prevention data.

Health experts have hailed vaccinations as the best source of protection against the virus, noting that the majority of people hospitalized with and killed by Covid-19 are unvaccinated. In Pennsylvania, from January 1 to September 7, 97% of the state's Covid-19 deaths were among unvaccinated people, Pennsylvania's acting secretary of health said Tuesday.

Another layer of strong protection, experts say, is masking.

The CDC recommends people -- even those fully vaccinated -- wear masks indoors in areas with substantial or high community transmission. More than 99% of the population lives in a county with one of those designations.

In Ohio, where children's hospitals are overwhelmed with Covid-19 and respiratory cases, Gov. Mike DeWine is encouraging schools to issue mask mandates since the state legislature has told him it would overturn any mandate he issued.

"Reasonable people may disagree about a lot, but we can all agree that we must keep our children in the classroom so they don't fall behind and so their parents can go to work and not take time off to watch their kids at home," DeWine said.

The combination of masks and vaccinations is the way to keep children in school, Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, told CNN on Tuesday.

"If you surround the kids with vaccinated people and you have everybody wear a mask, you can get a situation where the children will be relatively safe in school," Fauci told CNN's Jake Tapper.