(CNN) — First, the good news: The numbers of new Covid-19 cases each day in about 27 states have generally plateaued this past week compared to the previous week.

Now, the bad news: “Our levels are still far too high,” said Dr. Megan Ranney, an emergency physician at Lifespan Health System and associate professor at Brown University.

READ MORE: ‘Shut Up And Make Babies’: Protesters Reveal Deeply Personal Stories Following SCOTUS Decision

“We need those masks. We need those large social gatherings, honestly, shut down for the time being, until our country can come up with a comprehensive national strategy to get this virus under control.”

More than 4.6 million Americans have been infected with Covid-19, and more than 154,000 have died from the disease, according to data from Johns Hopkins University.

The relentless death toll is projected to reach 173,000 by August 22, according to a new composite forecast from the US Centers for Disease Control and Prevention. That’s an average of almost 1,000 US deaths every day for the next 30 days.

Across the country, public health experts are pleading for Americans to not let their guard down as social gatherings — especially among younger people — are fueling the crisis.

“What we are seeing today is different from March and April,” Dr. Deborah Birx, the White House coronavirus response coordinator, told CNN’s Dana Bash on Sunday. “It is extraordinarily widespread.”

Test positivity surges, but testing doesn’t

It’s not just recent spikes in new cases, hospitalizations and deaths that have doctors concerned. It’s also the test positivity rate — which is generally a good indicator of how rampantly the virus is spreading.

As of Sunday morning, the test positivity rate was rising in most states compared to last week, and 34 states had higher-than-recommended test positivity rates, according to Johns Hopkins.

“There are two things that are going on,” said Dr. Ashish Jha, director of the Harvard Global Health Institute.

“One is the underlying level of infection is rising, which is obviously the thing we are most concerned about,” Jha said.

“But in about 18 to 20 states, the number of tests that are being done is actually falling. And it’s falling because our testing system is under such strain that we just can’t even deliver the tests today that we were doing two weeks ago in about 18 to 20 states. That’s very concerning because when cases are rising, and your number of tests are falling, that’s a recipe for disaster.”

Going backward

The CDC says new deaths are likely to increase in Alabama, Kentucky, New Jersey, Tennessee and Washington. Some of these states previously reported progress in their Covid-19 numbers, but are facing trouble again.

In New Jersey, officials reported “an extraordinary milestone” Thursday — no new Covid-19 deaths in hospitals for at least 24 hours.

But Gov. Phil Murphy said the number of new Covid-19 cases jumped to an average of about 550 at the end of July — up from around 350 per day at the end of June.

“We are standing in a very dangerous place,” the governor said. New Jersey officers recently broke up a party of about 700 people, despite the state’s restrictions on gatherings.

“Everyone who walks around refusing to wear a mask or who hosts an indoor house party or who overstuffs a boat is directly contributing to these increases. This has to stop, and it has to stop now.”

In Louisville, Kentucky, the mayor reported another alarming trend. Almost 20% of coronavirus cases in the city — which now top 6,870 — were reported over seven days. Kentucky’s governor reported more than 570 new cases Saturday, including 11 infections that were in children 3 or younger.

Sunday, Gov. Andy Beshear announced 463 new cases, including 11 identified in children age 5 or younger, with Beshear lamenting, “we remain at war with the coronavirus.”

More masks ‘would really save a lot of lives in this country’

READ MORE: California Abortion Activists React To The End Of Roe V. Wade

Health officials say the best ways to curb this crisis are also some of the easiest: Avoid gatherings, stay at least 6 feet away from others and wear a mask.

Yet many people continue to ignore those guidelines, including some young people who are carrying the virus without symptoms and are infecting others unknowingly.

In Washington state, health officials said at least 30% of residents who tested positive for coronavirus caught it from someone who was asymptomatic.

Washington is one of at least 39 states that have some type of mask mandate in place. But even with the mandates, not nearly enough Americans needed to bend the curve for the infection rate are using face masks, one expert said Friday.

“We’re getting close to about 55% of Americans wearing a mask,” said Dr. Chris Murray, a researcher behind an influential coronavirus model from the University of Washington. “That’s good news, but of course it’s a long way to go before we get to the levels like Singapore has at 95%, which would really save a lot of lives in this country.”

Researchers in Texas reported that just two weeks of social distancing policies cut the spread of the virus by about 65% globally, preventing more than 1.5 million new cases.

“We found that states observed significant reductions in transmission rates following the implementation of social distancing policies, compared to states without such policies,” Daniel McGrail, a postdoctoral fellow studying systems biology, said in a statement.

“In fact, two of the smallest reductions in spread were seen in states without social distancing policies.”

More screening could control college outbreaks

With several outbreaks now linked to colleges and with some schools beginning to reopen, parents and local leaders are working to determine the safest options for the academic year.

Frequent screening of college students for the virus might be required in order to control outbreaks, according to a modeling study published Friday in the journal JAMA Network Open.

Researchers found that screening college students every two days — even with a low-quality test catching 70% of cases — is a cost-effective option, estimated to keep infections at a more controllable number than weekly testing with a higher-quality option.

For younger students, districts across the country have taken different approaches — some opting to go fully virtual for the beginning of the year and others offering hybrid options.

For example, Miami-Dade County Public Schools will continue virtual learning until at least October, Superintendent Alberto Carvalho told CNN affiliate WPLG. District officials “will revisit the conditions around September 30th for a possible return to the schoolhouse as early as October 5th, if the conditions are appropriate,” Carvalho said.

Asked Sunday whether schools in states with a 5% test positivity rate should remain closed or have distance learning, Birx said, “If you have high case load and active community spread, just like we are asking people not to go to bars, not to have household parties, not to create large spreading events, we are asking people to distance learn at this moment so we can get this epidemic under control.”

Birx did, however, defer to CDC guidelines on school reopenings.

Infected children younger than 5 have up to 100 times more genetic material from coronavirus in their noses than older children or adults do, according to a study published Thursday as a research letter in the journal JAMA Pediatrics.

“It says younger children up to 5 years old have many, many more times virus in their nasopharynx than adults do, which would mean it would be a reasonable assumption that they would be able to transmit the virus,” said Dr. Anthony Fauci, director of the National Institute for Allergy and Infectious Diseases.

“So they’re not immune.”

MORE NEWS: Tesla Fire In Alameda County Grows To Over 500 Acres

™ & © 2020 Cable News Network, Inc., a WarnerMedia Company. All rights reserved.