Respiratory viruses increasing as Americans prepare to gather for the holidays: CDC

Respiratory virus season has kicked off in the United States as Americans get ready to travel to celebrate the holidays.

Flu and COVID-19 emergency department visits and hospitalizations are continuing to increase throughout the United States, while vaccination rates lag, according to data from the Centers for Disease Control and Prevention.

Respiratory syncytial virus, or RSV, levels are still elevated in many areas of the country, although CDC data shows the weekly percent of total emergency department visits associated with RSV appears to be trending down after hitting its peak around Thanksgiving.

"[This is] good, so we don't have necessarily peaking of all of these simultaneous threats at the same time," said Dr. John Brownstein, an epidemiologist and chief innovation officer at Boston Children's Hospital, and an ABC News contributor. "At the same time, we are seeing a jump in COVID, which is not ideal because a new COVID variant, aligning with holiday travel and gatherings, is unfortunately [a] recipe for additional illness."

On Tuesday, the World Health Organization listed the JN.1 COVID variant -- a subvariant of the omicron variant -- as a "variant of interest." It is currently estimated to account for 21% of new cases in the U.S., according to the CDC.

There is currently no evidence to show that JN.1 causes more severe disease or that currently available treatments and vaccines are ineffective against the variant.

Countries in the midst of winter, such as the U.S., could see an increase in respiratory infections, the WHO said in a statement.

"That will unfortunately, over time, create some pressure on our health system," Brownstein said.

Some health systems in the U.S. are reinstating mask mandates due to the rise in respiratory viruses as they deal with an influx of patients.

UW Health, which primarily serves Wisconsin and northern Illinois, posted on X, formerly known as Twitter, on Tuesday that all staff, patients and visitors will be required to wear masks for patient interactions in clinic settings "due to expected seasonal increase and sustained high volume of respiratory illness."

Additionally, on Wednesday, masks became required at all University of Pittsburgh Medical Center facilities, according to Pittsburgh ABC affiliate WTAE. UPMC said cases would be monitored and protocols adjusted as necessary.

CDC Director Dr. Mandy Cohen recently told ABC News that, for the most part, pediatric hospitals have told the federal health agency they've been able to manage treating patients.

Brownstein said more hospitals may reinstate mask mandates in the coming weeks if cases do, in fact, rise following the holidays, but echoed Cohen's comments that hospitals have become better equipped to anticipate potential surges of patients.

"Hospitals have done a lot more to understand how to deal, especially with a new element of COVID as part of the seasonal mix," Brownstein said. "So, there is a lot more planning, forecasting and employee safety protocols, and it can ensure that hospitals are running at maximum capacity to handle a potential influx of patients."

Brownstein said he recommends the same mitigation measures that health officials have throughout the pandemic for those who are traveling or hosting for the holidays, including proper hand hygiene, being up to date on vaccines, improving ventilation and potentially masking, based on your personal risk level.

"Each individual household gathering is going to have a different mix of high-risk groups and vulnerable individuals, and we want to prepare to make sure -- especially for those that are potential, serious risk and complications -- that we're managing to overall reduce that risk," he said. "This is a playbook that we have gone to many times before, and so even though the impact of COVID isn't anywhere near where it used to be, everyone has the right tools to help reduce any potential risk of these respiratory pathogens heading into the holidays."

ABC News' Youri Benadjaoud contributed to this report.