Despite warnings, a flu season that wasn’t

As the nation suffered through a devastating winter surge of coronavirus cases, the phones at Old Dominion Pediatrics in Virginia rang off the hook. Callers with infected family members sought advice on ways to quarantine at home so others would not become ill.

But no one asked about the flu.

And the test results Eric Freeman was seeing showed that dozens of his patients had the coronavirus, but almost none were testing positive for influenza.

“COVID has just been the dominant viral pathogen right now, and it really has not allowed flu enough space to populate adequately,” Freeman said in an interview Monday. “I haven’t had a rapid flu test positive in my office since before Thanksgiving.”

Public health experts, general practitioners and pediatricians had warned for months that a surge in coronavirus cases over the winter months would be compounded by a typical flu season, which kills tens of thousands Americans annually. But a funny thing happened in the midst of a global health pandemic: Flu season was effectively canceled.

Data from the Centers for Disease Control and Prevention (CDC) shows just 1,893 Americans have tested positive for the influenza virus this year, between clinical laboratory results and public health labs. By this point last year, more than 290,000 people had tested positive for influenza.

The CDC reported in August that 198 children had died from influenza-related causes during the last flu season, a record high. So far this year, only one child has died, the lowest tally since records started being kept in 2004. 

“You’d never think there would be a silver lining to this [pandemic], but this is about as close to a silver lining as there has been,” said Peter Hotez, a pediatrician and dean of the National School of Tropical Medicine at Baylor College. “That’s what wearing masks and social distancing and probably reduced in-person classes [does].” 

Fewer than 1 in 1,000 hospitalizations this year have been for influenza, one-seventh the proportion recorded in the last low-severity flu season in 2011-2012. 

American health officials and vaccinologists typically glean key hints about the coming flu season from viruses that begin circulating in the winter months in the Southern Hemisphere, our summer months. 

But even as those officials were sounding the alarm about the potential for a double season of respiratory diseases, governments in Australia, Chile and South Africa were reporting lower-than-normal flu circulation. The viral curves in those three countries began to ebb far faster than in previous seasons, as new lockdowns and restrictions were put in place. 

“Over the past twelve months, with the exception of some countries in West Africa and some countries in Southeastern Asia, no one’s had a flu season. And that’s in countries that shut down really strictly, it’s in countries that maybe haven’t shut down as strictly. That confounds me a little bit,” said Richard Webby, director of the World Health Organization’s (WHO) Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds at St. Jude Children’s Research Hospital.

The same thing has appeared to happen in the United States. Influenza is less transmissible than the SARS-CoV-2 virus that causes COVID-19, meaning masks and social distancing likely has an even greater impact on the overall number of flu cases than on the coronavirus. School shutdowns meant curbing one of the most prolific vectors of person-to-person transmission.

“Young children and schools are pretty major players when we talk about transmission of flu in the community,” Webby said. “With a lot of schools not being open or the control measures actually being in schools, that’s had a major impact in influenza outbreaks.”

And, Freeman said, parents took to heart public health officials’ warnings that their kids should get a flu shot. Though final data on flu vaccine acceptance rates will not be known for months, Freeman said vaccine acceptance rates in his practice, just south of Richmond, Va., were substantially higher than in previous years.

“This was one of the best years I’ve had in 15 years of vaccinating against influenza. This year, parents were definitely engaged, very enthusiastic,” Freeman said. “It was to a point where I couldn’t keep flu vaccines on my shelves.”

Seemingly nothing about the coronavirus pandemic has been easy, and some experts warned that even the least harmful flu season on record could come with some drawbacks. A typical flu season provides clues about the strain that will become dominant next year, which then gives vaccine manufacturers the ability to tailor next year’s shots to a specific strain. Without that knowledge, it may be more difficult to produce a vaccine that matches next year’s strain.

“There is not enough information about the circulating virus in the world,” said Adolfo Garcia-Sastre, director of the Global Health and Emerging Pathogens Institute at the Icahn School of Medicine at Mount Sinai. “Because there is so little circulation of influenza, we don’t know exactly what strains, what variants are circulating now. That creates problems with development of the vaccine and whether it needs to be updated or not.”

David Wentworth, chief of the virology, surveillance and diagnosis branch of the CDC’s Influenza Division, said the WHO’s Global Influenza Surveillance and Response System is still testing between 50,000 and 100,000 samples per week to identify dominant strains.  

“The reduced number of positive specimens did make it more challenging to identify the optimal vaccine viruses for each of the four major groups of influenza viruses that are included in most influenza vaccines for the 2021-22 flu season, but it should be noted that the vaccine virus selection and recommendation process does not rely solely on influenza viruses currently in circulation,” Wentworth said in an email. 

Identifying the next strain also relies on genetic sequencing of current strains, post-vaccine serology studies to show which strains might break out next year, forecasting models and vaccine effectiveness studies.

The lack of a spike in influenza infections has reduced what could have been a crippling strain on the health care system at the height of the pandemic, when more than 100,000 Americans were being treated for COVID-19 in hospitals across the country. And the United States is still recording a huge number of deaths caused by what the CDC terms influenza-like illnesses — though in this case the overwhelming majority are because of COVID-19. 

The flu will not go away, and health officials are constantly keeping watch on worrying strains that could become the next threat to human health — the WHO said in January it is eyeing an outbreak of H5N6 in China, H1N1 cases in China and the Netherlands, H1N2 in Brazil and H3N2 in a child in Wisconsin. 

But the success of keeping influenza under wraps this year, doctors hope, will drive more acceptance of the vaccine that comes out over the late summer and early fall. 

“These [mitigation] measures are really working to reduce the spreading of infectious viruses that are respiratory,” Garcia-Sastre said. “I don’t think that we’ll reduce the cases enough to be able to completely prevent the spreading of the virus.”