By Christina Maxouris, CNN

(CNN) -- Experts say Covid-19 vaccinations in the US are continuing at an impressive pace, and now all Americans 16 and up can get a shot. But a leading health official said that the country remains in a "complicated stage" of the pandemic.

"More people in the United States are being vaccinated every single day at an accelerated pace," Centers for Disease Control and Prevention (CDC) Director Dr. Rochelle Walensky said during a White House Covid-19 briefing on Monday.

"On the other hand, cases and hospitalizations are increasing in some areas of the country and cases among younger people who have not yet been vaccinated are also increasing."

In the past seven days, the US reported an average of more than 67,100 new Covid-19 infections daily, according to Johns Hopkins University data. That's slightly below where the average was a week prior, but it's still 25% above where it was nearly a month ago.

And about 44,000 Covid-19 patients were in US hospitals as of Sunday, the most recent day that data was available, according to the US Department of Health and Human Services. That number has generally been inching up since late March, when it dipped to around 37,900.

Experts say there are several reasons the rise in these numbers, including dangerous coronavirus variants -- like the more contagious B.1.1.7 strain that has helped fuel another surge in Michigan. Pandemic fatigue and more Americans moving around have also likely contributed to the rise.

"People are tired," Matthew Budd, the director of Personal & Preventative Health Services in Jackson County, Michigan, told CNN over the weekend. "We've been through all these lockdowns, we've been cooped up and ... now that it's getting warmer out people are saying 'You know, we're just tired, we want to be outside, we want to be around other people.'"

John Fox, the CEO of Beaumont Health -- Michigan's largest health care system -- also recently told CNN it didn't help that states including Michigan recently eased Covid-19 restrictions.

In addition, Fox said, some people have strayed from safety measures that help curb the spread of the virus.

"I think people have dropped their infection control issues, they're not wearing their masks as much as they should, (or) social distancing, hand hygiene," Fox said.

What the CDC now recommends for the J&J vaccine

So far, more than 132 million Americans -- nearly 40% of the population -- have gotten at least one dose of a Covid-19 vaccine and more than 85 million -- roughly 25.7% of the population -- are fully vaccinated, according to CDC data.

After US officials recommended a pause on the J&J vaccine last week, the CDC is now recommending that people who experience certain new symptoms after receiving that shot seek immediate medical treatment.

Those may include a sudden and severe headache, backache, new neurological symptoms, severe abdominal pain, shortness of breath, leg swelling, tiny red spots on the skin and new or easy bruising.

The recommendation to pause came over six reported US cases of a rare and severe type of blood clot among more than 6.8 million Americans who got the J&J vaccine. While the vaccine is still authorized, the pause gives scientists time to review data and determine whether the vaccine is actually linked to the blood clots and, if so, whether recommendations on who should receive it should change.

The CDC says any adverse reactions should be reported through the Vaccine Adverse Event Reporting System.

After putting off a decision last week, vaccine advisers to the CDC will meet again Friday to take up the question of whether the J&J vaccine causes blood clots and if that's the case, what to do about it.

Johnson & Johnson believes that the benefits of its coronavirus vaccine outweigh risk, Dr. Paul Stoffels, the company's chief scientific officer, said during an earnings call on Tuesday morning.

"We continue to believe in the positive benefit/risk profile of our vaccine and in view of the raging pandemic that continues to devastate communities around the world, continue to collaborate with medical experts and global health authorities ... as we work towards continuing vaccination to end the global pandemic," Stoffels said.

The J&J vaccine was created differently from the Pfizer/BioNTech and Moderna vaccines.

About 78 million Americans have been fully vaccinated with the Pfizer/BioNTech or Moderna vaccines, and there have been no known cases of severe blood clots linked to either.

Colleges requiring Covid-19 vaccinations in fall

A growing number of colleges and universities across the US are announcing they'll be requiring Covid-19 vaccinations for students returning to campus in the fall.

More than 40 have announced the requirement, according to a CNN tally.

Yale University officials said in a letter to the university community on Monday that all undergraduate, graduate and professional school students are expected to be vaccinated before arriving on campus. If they can't receive a vaccine prior to return, the university said it will assist in making vaccine arrangements.

"Although the course of the Covid-19 pandemic over the coming months remains uncertain, vaccination is the strongest tool for preventing transmission of the virus," a letter from Yale University President Peter Salovey and Provost Scott Strobel said.

"There is abundant evidence of the vaccines' effectiveness and growing confidence that vaccines will be widely available by early summer," the letter added.

Columbia University made a similar announcement Monday, saying it will help provide vaccines to students who haven't been vaccinated.

"We regard this decision as essential to ensuring the health of Columbia students and the broader University and surrounding community, and also to containing the spread of the virus in New York City, one of the most severely affected locations in the country throughout this past 13 months," a letter from Columbia Senior Executive Vice President Gerry Rosberg and the university's Covid Director Donna Lynne said.

The university said it has sites offering the Pfizer and Moderna Covid-19 vaccines.

Another ban on Covid-19 vaccine passports

The university announcements come amid ongoing debates in different parts of the country on whether vaccinations should be mandated in certain spaces.

The debate mostly centers around a so-called vaccine passport, which is proof that a person has been immunized against Covid-19.

On Monday, Arizona Gov. Doug Ducey issued an order banning vaccine passports and preventing state and local governments from requiring residents to provide their Covid-19 vaccination status to receive a service or enter a certain area.

"The residents of our state should not be required by the government to share their private medical information," the governor said in a statement. "While we strongly recommend all Arizonans get the Covid-19 vaccine, it's not mandated in our state -- and it never will be. Vaccination is up to each individual, not the government."

Florida Gov. Ron DeSantis has also banned the use of Covid-19 vaccine passports in the state, citing freedom and privacy concerns for doing so.

"It's completely unacceptable for either the government or the private sector to impose upon you the requirement that you show proof of vaccine to just simply be able to participate in normal society," DeSantis previously said.