The flu all but disappeared for two years as the pandemic raged. But the flu looks set to make a comeback this year in the United States, threatening to cause a dreaded “double epidemic.”
Although the flu and the coronavirus are both notoriously unpredictable, there’s a good chance that COVID cases will rise again this winter, and there are troubling signs that the flu could return as well.
“This could very well be the year we see a twindemic,” says Dr. William Schaffner, professor of infectious diseases at Vanderbilt University. “That is, we have an increase in COVID and simultaneously an increase in flu. We could have both affecting our population at the same time.”
The strongest indication that the flu could hit the United States this winter is what happened during the Southern Hemisphere winter. The flu has returned to some countries, such as Australia, where respiratory infection began to rise months earlier than normal and caused one of the worst flu seasons in years.
What happens during the southern hemisphere winter often foreshadows what will happen north of the equator.
“If we have a severe flu season and if omicron variants continue to cause mostly mild illness, next winter could be a much worse flu season than COVID,” Schaffner warns.
And the combination of the two viruses could put a strain on the healthcare system, he says. The Centers for Disease Control and Prevention estimate that the flu causes between 140,000 and 710,000 hospitalizations per year.
“We should be worried,” says Dr. Richard Webby, an infectious disease specialist at St. Jude Children’s Research Hospital. “I don’t necessarily think it’s a race for the worried hills. But we have to be worried.”
The main reason the flu has all but disappeared over the past two years was the behavioral changes people made to avoid COVID, such as staying home, avoiding public gatherings, wearing masks, and not traveling. It also prevented flu viruses from spreading. But these measures have mostly been abandoned.
“As community mitigation measures begin to roll out around the world and people return to their normal activities, influenza has begun to circulate around the world,” says Dr Alicia Fry, who leads epidemiology and flu prevention for the CDC. “We can expect a flu season this year for sure.”
Young children at high risk
The CDC reports that the flu is already beginning to spread in parts of the South, such as Texas. And experts warn that very young children could be particularly at risk this year.
Although COVID-19 has generally been mild for young people, the flu generally poses the greatest threat to the elderly and children. The main flu strain currently circulating, H3N2, tends to hit older people hard. But health experts are also worried about young children who haven’t been exposed to the flu for two years.
“You have the 1-year-olds, the 2-year-olds, and the 3-year-olds who will all be seeing it for the first time, and none of them have pre-existing immunity to the flu,” says Dr. Helen Chu, assistant professor of medicine and allergy and infectious diseases and adjunct assistant professor of epidemiology at the University of Washington.
In fact, the flu seems to have hit young people in Australia particularly hard.
“We know schools are really where the flu spreads. They’re really seen as the engines of transmission,” Chu said. “They’ll be the spreaders. They’ll then bring it home to the parents. The parents will then bring it to the workplace. They’ll bring it to the grandparents who are in assisted living, in a nursing home. And then these populations will then become seriously ill with the flu.”
“I think we’re heading into a bad flu season,” Chu says.
‘Virus interference’ could outweigh the risks
Some experts doubt that COVID and the flu hit the country simultaneously due to a phenomenon known as “viral interference,” which occurs when infection with one virus reduces the risk of catching another. This is one more possible reason why the flu has disappeared for the past two years.
“These two viruses can still both happen in the same season, but my hunch is that they’re going to happen sequentially rather than both at the same time,” Webby says. “So I’m less concerned about the twindemic.”
Still, Webby and others urge people to make sure all family members get their flu shot as soon as possible, especially if flu season is also coming early in the United States. (In most years, officials don’t start pushing people to get the flu shot until October.)
So far, it looks like this year’s flu shots are a good match to circulating strains and should therefore provide effective protection.
But health officials fear fewer people are getting their flu shots this year than usual due to anti-vaccine sentiment that has grown in reaction to COVID vaccinations. Flu vaccination rates are already lagging.
“We’re concerned that people won’t be vaccinated. And the flu shot is the best prevention tool we have,” said the CDC’s Fry.
Fry also hopes that some of the habits people have developed to fight COVID will continue and help lessen the impact of the flu.
“The wildcard here is that we don’t know how many mitigation practices people will use,” Fry says. “For example, people now stay home when they are sick instead of going to work. They prevent their children from going to school. Schools are strict about not letting children come to school. if they’re sick. All of those types of things could reduce transmission.”