June 14, 2021 -- 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.

For a while it seemed the pandemic had tamped down some of the more typical seasonal viral illnesses. Some of the indications have been anecdotal, notably about fewer flu and respiratory syncytial virus (RSV) infections.


But now the data is coming in. The CDC has issued a health advisory to notify doctors and caregivers about an increase in cases of RSV across parts of the southern United States.

With this increased activity, the CDC urges broader testing for RSV among patients with respiratory illness who test negative for coronavirus.

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, says 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 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, showed sharp increases in seasonal respiratory viruses, including RSV, in Houston, Texas, after relaxing COVID-19 restrictions. The study has not yet been peer reviewed.

Researchers found that RSV cases increased 166% by May 25 when compared to 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.

From Nothing to Many

Costi Sifri, MD, director of hospital epidemiology at University of Virginia Health in Charlottesville, says 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 seeing few during the pandemic.

He also said that after a year of few non-COVID infections, some patients may end up infected with multiple viruses at once..

In a very rare example, he said, this week an infant at University of Virginia 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 says.

While he says 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 notes 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 other sanitizing habits 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 says.

According to CDC data, U.S. health labs confirmed just 2,150 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.

Maximo Brito, MD, professor of medicine at the University of Illinois at Chicago, and says he doesn’t see increased threats but a normal return to prepandemic levels.

Doctors, 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 says .

The CDC has developed a test that will check for A and B type seasonal flu viruses and coronavirus at the same time. The test will be used by 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 FDA 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 says 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 about 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."