The most contagious delta variant of the coronavirus now accounts for 83% of new cases in the United States.

(CNN) – The most contagious delta variant of covid-19 now makes up 83% of sequenced samples in the United States, Dr. Rochelle Walensky, director of the US Centers for Disease Control and Prevention, said Tuesday. (CDC).“This is a drastic increase, up from 50% for the week of July 3,” Walensky said at a Senate committee hearing.

Health experts have said that the delta variant is more transmissible than any other variant identified so far. “We should think of the delta variant as the 2020 version of COVID-19 on steroids,” Andy Slavitt said, Former Senior Advisor to Joe Biden’s COVID Response Team, told CNN last week.

“It is twice as infectious,” Slavitt said. “Fortunately, unlike in 2020, we have a tool that stops the delta variant in the bud – it’s called a vaccine.”

However, vaccination rates in the country have stagnated. Less than half of the American population is fully vaccinated, according to CDC data, and the majority of those who are not vaccinated are unlikely to do so. According to a survey Posted Tuesday by Axios-Ipsos.

A quarter or fewer of those who are not vaccinated said they would be likely to be vaccinated under certain circumstances, according to the survey, conducted July 16-19 and comprised of a nationally representative sample of 1,048 American adults. of the general population.

If many of those who wait do not get vaccinated, said Dr. Anthony Fauci, the United States can expect a “suffocating” outbreak for “a considerable period of time.”

The rise in the delta variant comes at a time when the US is registering a new spike in COVID-19 cases and an increase in hospitalizations and deaths, especially in areas of the country where vaccination rates remain relatively low.

This week’s average new daily cases is up 66% from last week and 145% from two weeks ago, as cases rise in 44 states, according to data from Johns Hopkins University. In addition, hospitalizations have increased 26% compared to last week.

Vaccines are effective against the delta variant

The most recent data, from Israel, evaluating the efficacy of the mRNA covid-19 vaccine produced by Pfizer / BioNTech against the delta variant, indicate that the vaccine protects 64% against infection, and that it is a 93% effective in preventing serious illness and hospitalizations.

Other studies indicate that Moderna and Johnson & Johnson’s covid-19 vaccines are also effective against the delta variant.

And 99.5% of deaths are among the unvaccinated, US surgeon general Dr. Vivek Murthy told Dana Bash on CNN’s “State of the Union” on Sunday, a figure cited. by the CDC at the beginning of the month.

Some hospitals are already overrun with COVID-19 patients again, Murthy said Monday.

“I am heartbroken to see how hard (the doctors) are working, how exhausted they are,” Murthy told CNN’s Anderson Cooper.

“Many of them are suffering with depression, anxiety, post-traumatic stress disorder, suicidal ideation, as a result of the stress they have endured during this pandemic.”

Having been fooled by the virus before, Murthy says now is the time to be cautious.

“There have been multiple times that we’ve been misled by COVID-19, when cases went down and we thought we were safe and then cases went back up,” Murthy said. “This means that we must not let our guard down until cases are not just down but are staying low, and right now cases are going up. Cases are going up, hospitalizations are going up, death rates are going up.”

Murthy urged Americans to get vaccinated, if not for themselves, then for healthcare workers who need protection from burnout and for children who cannot yet benefit from the protection offered by the vaccine.

Even if parents are vaccinated, wearing a mask in high-risk areas for transmission is “the right thing to do,” he said. Murthy, a father of two boys ages 3 and 4, said he takes these precautions because “I want to take all possible steps to protect my children.”

“Our children, who cannot get vaccinated, depend on us being vaccinated to protect them from the spread of the virus. We are their shields,” Murthy said. “Even if you don’t want to do it yourself, consider getting vaccinated to protect the children in your community. They depend on us.”

The pediatric association recommends the use of masks in schools

In addition to protecting children from contagion, many experts and officials have stressed the importance of their safe return to classrooms.

Most children are at a lower risk than adults of contracting a serious illness from COVID-19, and the benefits of learning in a classroom outweigh the risks, said Dr. Greta Massetti, a member of the Emergency Response to Covid- 19 from the US Centers for Disease Control and Prevention.

“However,” he added, “for some families, particularly those with children or family members who are at increased risk of serious illness from COVID-19, or who cannot get vaccinated, those families may feel more comfortable with a remote option this fall. “

On Monday, the American Academy of Pediatrics (AAP) released a new guide for schools that supports in-person learning and recommends universal use of masks in schools for all ages 2 and older.

“The AAP believes that, at this point in the pandemic, given what we know about low rates of transmission at school when appropriate prevention measures are used, along with the availability of effective vaccines for those 12 and older , the benefits of face-to-face school outweigh the risks in all circumstances, “says the guidance.

The guide differs in part from the CDC recommendations, which advise the use of masks in schools for all people who are not fully vaccinated.

But Fauci said the CDC leaves flexibility for localities to make decisions based on their situation.

And when there is a high rate of spread of the virus in a community and a low proportion of vaccinated people, “you really want to go an extra step to make sure that there is not a lot of transmission, even post-vaccination infections among vaccinated individuals.” Fauci said. “They just want to be more secure.”

Some states, such as Connecticut, Hawaii, New Mexico, New York, Virginia, and Washington, follow AAP guidelines and require the use of masks for students from preschool to 12 years of age, regardless of their immunization status.

But an updated CNN analysis found that at least nine states – Arkansas, Arizona, Georgia, Iowa, Oklahoma, South Carolina, Texas, Utah and Vermont – have enacted laws prohibiting districts from requiring masks in schools.

Local leaders urge residents to put on masks again

While some states are staying away from mask-wearing mandates, others are adopting a return to preventative measures.

As California reports an increase in cases to levels not seen since February, when new cases fell after a winter surge, about half of the state’s population is once again subject to mask mandates and recommendations. .

“This is inevitable,” California Governor Gavin Newsom said of the new requirements and recommendations. “If we want to end this pandemic once and for all, if we want to turn the page, we can do it in a matter of weeks, not months. It’s as simple as this: If you are not vaccinated, get vaccinated.”

In Massachusetts, Provincetown authorities issued a public health advisory Monday advising the public to resume wearing face masks and get vaccinated if they haven’t already. The public health advisory comes amid a surge in cases in Provincetown after the July 4 weekend, according to the notice.

The advisory also states that “high-density places where physical distancing is not possible are strongly advised to verify vaccination status prior to admission.”

New Jersey is also seeing an increase in rates, with a positivity rate that has increased to 2.5% and an increase of 20% in unvaccinated patients in hospitals, according to the Commissioner of Health. from the state, Judy Persichili.

But the state will not resume the mask use mandate for now.

“We are still comfortable where we are, but we watch this like a hawk. And our strong, strong preference is not to go back,” Gov. Phil Murphy said.

– CNN’s Deidre McPhillips, Lauren Mascarenhas, Sarah Braner, Naomi Thomas, Jacqueline Howard, Elizabeth Stuart, Cheri Mossburg, Kay Jones and Christina Bowllan contributed to this report.