By Amir Vera and Eric Levenson, CNN

(CNN) -- Declines in the average number of daily Covid-19 deaths and in new cases indicate that the virus' summer surge through the US is waning.

The 7-day average of coronavirus deaths dropped below 1,000 a day over the weekend for the first time since late July. Also, the average number of new cases dipped to about 42,600 as of Sunday, well below its peak in mid-July of around 67,000 daily cases, according to data from Johns Hopkins University.

Although the trends are in the right direction, the US remains the world leader in total cases and deaths. For comparison, the European Union is experiencing a worrying surge in coronavirus; on Sunday, all 27 countries reported a total 7-day average of 17,000 new cases per day.

Will these US declines continue? And how low will the totals go?

The answers to those questions are complicated by the planned reopening of schools, which has already led to outbreaks at universities in at least 19 states.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said earlier this month that he wanted to see cases drop below where they were in spring.

"When you look at our curve, it's telling. And that's the thing that bothers me. We went way up and we came down. We came down to a plateau of 20,000 cases per day. That is not a good baseline. We needed to get further down," Fauci said on August 5.

College campuses become new hotspots

Many outbreaks are tied to large group gatherings like parties, leading some schools to suspend students and organizations for breaking social distancing rules on and off campus.

The University of Notre Dame and the University of Alabama both have seen increases in Covid-19 cases on their campuses. Notre Dame has moved to online instruction, according to its website. Meanwhile, local and university police at the University of Alabama will partner to monitor bars, restaurants and off-campus housing to ensure the city's Covid-19 ordinances and university guidelines are followed, university President Stuart R. Bell said.

"Violations to our health and safety protocols, both on and off campus, are subject to harsh disciplinary action, up to and including suspension from UA," Bell wrote in a letter to the campus community on Sunday.

The University of Kentucky began a second phase of testing Sunday after a roughly 3% positivity rate for Covid-19 among fraternities and sororities in initial testing, which is triple the roughly 1% positivity rate for the general student population. And Central Michigan University has threatened to fine or suspend students who host large gatherings.

Penn State suspended its second fraternity this week for social distancing violations, according to a Sunday statement from the university.

Pi Kappa Alpha has been suspended for "hosting a large social gathering" on Saturday, that included about 70 students, the university said. The Phi Kappa Psi fraternity was previously suspended from the campus following an August 18 gathering that violated school policy, the university said.

Despite the rise in cases, University of Kentucky President Eli Capilouto cautioned against blaming students for the higher positivity rate on the school's campus.

"Let me be clear: This is not an act to blame the students who reside in these facilities or who belong to these organizations," he wrote. "We believe a number of factors associated with communal living spaces likely contributed to the high positivity rates in these residences."

Across the US, there are 5.7 million cases of coronavirus and more than 176,000 people have died, according to the JHU database.

Concerns and questions about the new school year

On the K-12 front, school districts are still trying to figure out how to navigate the academic year during the pandemic.

Many schools across the country have implemented increased measures to protect students and staff against the virus, even though researchers are still learning how the virus spreads among young children.

The US Centers for Disease Control and Prevention updated its school guidance Friday emphasizing the importance of keeping schools open if possible. One big change in the guidelines was how schools can handle a positive case.

The CDC encouraged schools to work closely with local and public health leaders if there is an infected person on campus. But rather than shut everything down immediately for a long period of time, the guidelines said one option is an initial short-term class suspension and cancellation of events and after-school activities, so that public health leaders can get the time they need to determine how widespread the infections are.

If schools are using a pod system, keeping certain students together, administrators may only need to close certain parts of the building where an infected person had been.

A school district in Michigan canceled all classes and after-school activities for Monday -- its first day of school -- after "receiving a threat" on Sunday, according to an alert on the district's website.

The Leslie Public Schools District did not offer details on the nature of the threat, but said it will work with law enforcement to assess it.

In Florida, a 6-year-old girl became the youngest person in the state to die from coronavirus complications. Health officials say they still don't know if the child contracted the virus from a known case or if it was travel related.

Convalescent plasma for Covid-19 treatment

The US Food and Drug Administration issued an emergency use authorization Sunday for convalescent plasma for the treatment of Covid-19 in hospitalized patients.

Convalescent plasma is created from the blood of people who have recovered from Covid-19, and it has shown some success in two other deadly coronaviruses: MERS and SARS. It has also been used to treat flu and Ebola.

The agency said it concluded that it may be effective in treating Covid-19 and that "the known and potential benefits of the product outweigh the known and potential risks of the product."

Some experts, however, say there is not enough solid data to support the use of the plasma.

"The problem is, we don't really have enough data to really understand how effective convalescent plasma is," Dr. Jonathan Reiner, a professor of medicine at George Washington University and a CNN medical analyst said Sunday.

Art Caplan, founding head of the Division of Medical Ethics at NYU School of Medicine, told CNN he's worried about whether there's a large enough supply of convalescent plasma, which relies on donations from Covid-19 survivors.

"We're going to get a gold rush towards plasma, with patients demanding it and doctors demanding it for their patients," Caplan said.

Trump administration officials cited a Mayo Clinic-led study that showed a 35% improvement in survival among people given the highest doses of the treatment early on in their illness compared to those who were treated later.

FDA commissioner Dr. Stephen Hahn says studies have shown convalescent plasma is safe and the treatment has been given to patients with infectious diseases for more than a hundred years.