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It’s not just people coming out of lockdown: As COVID-19 restrictions ease and masks come off, as crowds gather and vacationers travel, viruses that had been reduced, in some cases to negligible threats, are reemerging.

Some of the indications of fewer viral illnesses have been anecdotal, notably about influenza and respiratory syncytial virus (RSV) infections.

Exactly. Never in my 22 year career have I seen zero cases of flu or RSV in an entire winter. It’s been almost a year since we saw flu here.
I’ve seen one case of bad croup and that’s it. Nothing. Nada. Zero. Zilch.

— Dr. Jaime Friedman (@DrJaimeFriedman) March 6, 2021

But now the data is coming in. The Centers for Disease Control and Prevention (CDC) has issued a health advisory to notify clinicians and caregivers about an increase in cases of interseasonal RSV across parts of the southern United States.

With this increased activity, the CDC urges broader testing for RSV among patients presenting with acute respiratory illness who test negative for SARS-CoV-2.

The CDC noted increases in positive RSV tests in Alabama, Arkansas, Florida, Georgia, Kentucky, Louisiana, Mississippi, New Mexico, North Carolina, Oklahoma, South Carolina, Tennessee, and Texas.

Viruses Coming Out of Lockdown Too

RSV is more commonly seen in the fall and winter, so its early emergence is troubling, says pediatrician Martha F. Perry, MD.

Perry, associate professor and medical director at the University of North Carolina Children’s Primary Care Clinic in Chapel Hill, told Medscape Medical News that, with so many viruses kept at bay with COVID-19 mitigation efforts, they now may start circulating simultaneously.

“We are seeing an increase in presentation to our primary care clinics, our emergency room and urgent care settings with viral-type illnesses,” she said.

“The concern is,” she added, “are we going to see a summer and winter wave at the same time?”

Perry said that experts are keeping a close eye on RSV in the United States because Australia, where seasons are opposite those in the United States, already saw summer spikes in RSV after COVID-19 restrictions lifted there.

The Jewish Telegraphic Agency also reports on a recent outbreak in Brooklyn of RSV. According to the city’s health department, there were 10 documented cases of RSV in Brooklyn during the last week of February. From April 4 through April 10, there were 294.

A study by Parsa Hodjat, published in the preprint medRxiv and not peer-reviewed, showed sharp increases in seasonal respiratory viruses, including RSV, in Houston, Texas, after relaxing COVID-19 restrictions.

Researchers found that RSV cases increased 166% by May 25 when compared with cases in April.

Parainfluenza — a common virus that can cause respiratory illnesses such as colds, bronchitis, croup, and pneumonia — rose 424% in Houston from March to April, the study found. It also increased 189% from April through May 25.

Seasonal coronaviruses, which typically emerge in the winter and decline in March, increased by 211% in Houston from March to April and continued to increase in May.

Rhinovirus and enterovirus cases were up 85% in Houston from March to April.

Concern for Newborns

Perry said there is also concern around immunity usually transferred to fetuses in utero but potentially compromised when mothers’ exposure to viruses has been subdued.

If pregnant women haven’t been exposed or had only mild infections while they were pregnant or just prior to being pregnant, the usual immunity is not going to get passed to the infant, Perry said.

“That’s where we may see more severe infection,” she said.

Dr Costi Sifri

Costi Sifri, MD, director of hospital epidemiology at University of Virginia Health in Charlottesville, told Medscape Medical News that at one point this winter his hospital had zero cases of flu and very few RSV cases.

Recently, he said, he has been seeing an increase in cases of parainfluenza after a dearth of cases during the pandemic.

He also said that coinfection of respiratory viruses may be a consequence of a year with few cases.

In a very rare example, he said, this week an infant at UVA Health was hospitalized with parainfluenza, adenovirus, RSV, and rhinovirus/enterovirus at the same time.

“I’ve never seen any patient, any child, with four different respiratory viruses at the same time,” Sifri said.

While he said that would likely continue to be very rare, “multiple respiratory viral infections at the same time are certainly possible, particularly as people go back indoors in the fall and are not wearing masks.”

He noted that while transmissions of COVID-19 are rare on surfaces, it is not uncommon for other viruses to be passed that way, so slacking off on handwashing or relaxing sanitizing measures could invite a boost in non-COVID respiratory infections.

He said it’s possible that people who escaped the usual colds and flu through the pandemic could be more susceptible to reemerging viruses, but it’s too early to tell.

With the uncertainty, “It will behoove us to really promote influenza vaccination,” Sifri said.

According to CDC data, US clinical health labs and public health labs confirmed just 2150  flu cases between September 27, 2020, and May 29, 2021 (though the true number of people who got the flu was likely higher).

For comparison, between October 2019 and April 2020, the CDC estimated that at least 39 million people contracted the flu.

Dr Maximo Brito

Maximo Brito, MD, professor of medicine, University of Illinois at Chicago, and Chief of Infectious Diseases, Jesse Brown VA Medical Center in Illinois, told Medscape Medical News he doesn’t see increased threats but a normal return to prepandemic levels.

Clinicians, however, will have more diagnostic challenges.

Whereas now “every flulike illness that walks into the emergency room is COVID until proven otherwise,” other respiratory diseases will need to be given serious consideration again, he said.

The CDC has developed a test that will check for A and B type seasonal flu viruses and SARS CoV-2 at the same time. The test will be used by US public health laboratories. Testing for the viruses at the same time will give public health officials important information about how flu and COVID-19 are spreading and what prevention measures are necessary.

The US Food and Drug Administration has given the CDC Emergency Use Authorization for the combined test.

The CDC recommends that all people 6 months and older get a yearly flu vaccine.

Brito said that predicting what strains vaccines will need to protect against will be more difficult because the flu has been so subdued during the pandemic.

He said he is also worried that the amount of misinformation circulating with COVID-19 will make people even more reluctant to get the flu vaccine this next season. Last season, only 49.2% of Americans got a flu shot.

Brito said he is seeing people in his practice who never questioned routine vaccinations in the past becoming hesitant now.

“I worry they will make the wrong choices in the future,” he said. “I hope I’m wrong.”

Perry, Sifri, and Brito report no relevant financial relationships.

Marcia Frellick is a freelance journalist based in Chicago. She has previously written for the Chicago Tribune, Science News, and Nurse.com, and was an editor at the Chicago Sun-Times, the Cincinnati Enquirer, and the St. Cloud (Minnesota) Times. Follow her on Twitter at @mfrellick.

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