The seasonal flu was all but MIA this season. Here’s why

Published on Monday, March 1, 2021

By: Gary Pettus, gpettus@umc.edu

It may be hard to believe that the soon-to-be extinct, pandemic- and ice-packed winter of 2020-2021 might have been worse.

But infectious disease experts had feared a double whammy of an outbreak brought on by overlapping bouts of COVID-19 and seasonal influenza – a “twindemic” that never materialized when the flu barely showed its feverish face

“Usually, the flu season peaks in Mississippi in January and February,” said Dr. Bhagyashri Navalkele, assistant professor of medicine and medical director of infection prevention and control at the University of Mississippi Medical Center. “We have not seen that large number of cases, compared to the previous two seasons.

“All across the U.S., we are seeing very low numbers.” Mississippi is among the vast majority of states, where, the Centers for Disease Control and Prevention reports, flu activity is "minimal."

Navalkele is among those who say there are several reasons for this. Not least of all are the precautions many took to heart to prevent the spread of COVID-19.

Apparently, physical-distancing, mask-wearing, hand hygiene and environmental cleaning helped foil the flu.

“Yes, absolutely, all of that contributed,” Navalkele said. “People were vaccinated for the flu, as they are every season, and there were upticks in the vaccination rates. But the precautionary measures were not common in previous years.”

For the period between Sept. 27, 2020 and Feb. 20, 2021, the number of positive influenza tests in the U.S. reported to the CDC  was 1,499 – out of 659,131 specimens, or 0.2 percent.

To compare that with the 2019-2020 season: A national summary revealed that, of more than 493,000 specimens tested then, almost 64,000 were positive, or 13 percent.

As for the flu hospitalization rate for the 14 states reporting: In 2011-2012, considered a mild flu season, it was 2.2 times higher, compared to the same time this season: between October 1, 2020 and Feb. 20, 2021, the CDC reports.

Also last flu season, the CDC calculated that in the United States the virus sickened 38 million people – the approximate population of Poland, and 128 times the population of Mississippi; it took the lives of 22,000. The CDC also estimated that, for that 2019-2020 season, which ended September 19, influenza was linked to the deaths of at least 434 children.

For Mississippi, individual flu cases and lab results are not “specifically reportable,” according to the Mississippi State Department of Health, which relies on selected “sentinel” health practitioners to gauge the flu’s geographic spread. As of late last week, MSDH had not recorded a single lab-reported case this year.

Pediatric flu deaths are reportable, though, and for this flu season, so far, one pediatric death has been reported in this country. “Which is extremely remarkable,” Navalkele said.

“Usually, we see around 150 to 200.”

School closings, and the safeguards applied once schools re-opened, may have had much to do with slowing the spread of influenza, which subjects its victims to a fever of 100°F or higher and cough or sore throat.

“The lockdown of schools and early childhood education centers has contributed,” said Dr. April Palmer, professor of pediatrics and chief of the Division of Pediatric Infectious Diseases at UMMC. “Lockdowns of businesses, too, have decreased crowding.”

In fact, though, children may have been more protected at school than in their own homes, as some experts have suggested, at least in those where social-distancing and other protections were taken seriously.

“At home, children are more likely to crowd together with others,” Palmer said. “And they are less likely to wear masks and be separated by six feet.

“Also, influenza is mainly spread through contact with droplets. So, mask-wearing can help prevent that. Children have been better at wearing masks than we thought they would be.

“And the schools have put a lot of emphasis on cleaning the environment and hand hygiene, which prevents the spread of any virus.”

Bearing that out: Viruses other than the flu have had an off-year as well, said Dr. Joyce Olutade, assistant professor of family medicine at UMMC.

For the Respiratory Syncytial Virus Infection, or RSV, positive tests in the U.S. have fallen by about 90 percent. For the week ending Feb. 20, 2021, for example, there were zero positive tests, Olutade said. While a usual case of RSV means mild, cold-like symptoms, the virus can be more menacing, especially for infants and older adults.

Confirmed cases also plunged for another condition, acute flaccid myelitis, which usually peaks every other year between August and November: 30 in 2020, compared to 238 in 2018, and 153 in 2016, Olutade said. AFM, preceded by a viral infection, is relatively rare but sinister, causing sudden weakness in the limbs, along with loss of muscle tone and reflexes, mainly in young children.

And, of course, for influenza, the number of cases is also unusually low.

“It’s been amazing how these public health measures have reduced the flu,” Olutade said.

But why did they work better on influenza, when balanced against the terrible toll of COVID-19?

Because COVID-19 is more contagious, or transmissible, than the seasonal flu, Olutade said. There’s even a formula to show that, with a figure called R0. It stands for how many new cases, on average, each case of a disease will spawn.

“For the seasonal flu, the R0 is 1.28,” Olutade said. For COVID-19, the average is between 2 and 3.5. “In certain communities, when public health measures are not being observed, it can be much higher,” she said.

In other words, it’s easier, for now, to wipe out the flu than it is COVID-19. 

Speaking of which, other factors may have helped cause the flu to fizzle. In the U.S., we use the Southern Hemisphere as a crystal ball: A severe flu season there, during our own hemisphere’s summer, could foretell a severe season in the U.S. starting in the fall.

“Last summer, the Southern Hemisphere had very few cases,” Olutade said. So, a mild season may have been in the cards for the U.S. anyway.

At any rate, Navalkele said, “you should be careful comparing COVID with the flu. We had never seen COVID before, so the whole population was susceptible to it.

“The flu has been with us many years; people have been getting vaccinated against it. But, for COVID, we still have a large population which is not immune to it. Many people have not been vaccinated against it. And the variant that’s coming could force up the numbers.

“Also, many people have had the flu, so there has been some natural immunity to it for a long time.”

That raises the question: What degree of immunity will we have come next flu season, when so few people caught the flu this season? Is the silver lining, vis-à-vis influenza, about to be tarnished?

“When a virus is novel, when there has been less exposure to it, there is little or no immunity, and you tend to have more cases,” Palmer said. “But the Pollyanna view is that maybe we have learned from this pandemic how to prevent the spread of all viruses. So the next season may be mild.”

Which raises another question: Even post-pandemic, should we continue these socially- and politically-fraught deterrents to slow the spread of not only COVID-19, but also the flu?

“Whenever you are in a closed space, such as during air travel, wearing a mask and other measures are a good idea at all times, not just during a pandemic,” Olutade said.

“That’s especially true for the elderly when they are going be in close contact with others. So it’s also a good idea to do this in nursing homes.”

Since these defenses work and have helped prevent the spread of other respiratory diseases as well, Navalkele said, “next flu season, it might be that we ask people to wear masks and to continue social distancing and hand hygiene, along with getting a vaccination.”

The public’s taste, or lack thereof, for upholding social distancing may raise the biggest challenge, Palmer said.

“Keeping six feet apart will probably be the most difficult to maintain, especially as we try to get children back in all the schools. It means you can have only a certain number of children in one room.

“But I hope we can continue to practice hand hygiene and environmental cleaning to reduce infections in children. And, especially during a bad outbreak, we could present mask-wearing as an option to closing down a school.”

No matter what we do, or don’t do, Navalkele has an urgent request, or two: “For anyone who hasn’t received their flu shot, please get one, especially those in a high-risk group.

“Also, you should get the COVID vaccine.”