Last fall, health experts said it was possible the United States could experience an easy 2020-21 flu season because health measures to fight COVID-19 would also thwart the spread of influenza.
It looks like that happened – and then some. Numbers are strikingly low for cases of the flu and other common respiratory and gastrointestinal viruses, health experts told the Washington Post.
“It’s crazy,” Lynnette Brammer, MPH, who leads the domestic influenza surveillance team at the Centers for Disease Control and Prevention, told the Washington Post. “This is my 30th flu season. I never would have expected to see flu activity this low.”
Influenza A, influenza B, parainfluenza, norovirus, respiratory syncytial virus, human metapneumovirus, and the bacteria that cause whooping cough and pneumonia are circulating at near-record-low levels.
As an example, the Washington Post said in the third week of December 2019, the CDC’s network of clinical labs reported 16.2% of almost 30,000 samples tested positive for influenza A. During the same period in 2020, only 0.3% tested positive.
But there’s a possible downside to this suppression of viruses, because flu and other viruses may rebound once the coronavirus is brought under control.
“The best analogy is to a forest fire,” Bryan Grenfell, PhD, an epidemiologist and population biologist at Princeton (N.J.) University, told the Washington Post. “For the fire to spread, it needs to have unburned wood. For epidemics to spread, they require people who haven’t previously been infected. So if people don’t get infected this year by these viruses, they likely will at some point later on.”
American health experts like Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Disease, said last fall that they noticed Australia and other nations in the southern hemisphere had easy flu seasons, apparently because of COVID protection measures. The flu season there runs March through August.
COVID-19 now has a very low presence in Australia, but in recent months the flu has been making a comeback. Flu cases among children aged 5 and younger rose sixfold by December, when such cases are usually at their lowest, the Washington Post said.
“That’s an important cautionary tale for us,” said Kevin Messacar, MD, an infectious disease doctor at Children’s Hospital Colorado, Aurora. “Just because we get through the winter and don’t see much RSV or influenza doesn’t mean we’ll be out of the woods.”
A version of this article first appeared on WebMD.com.