Social distancing has nearly extinguished the spread of influenza and other respiratory viruses. But that means future outbreaks could be severe — and may come at weird or unexpected times, experts are warning.
In the short-term, fewer cases of flu mean fewer flu deaths and hospitalizations, taking some burden off the health care systems already slammed with COVID-19, The Atlantic reported. Cases of other seasonal viruses, including respiratory syncytial virus (RSV), common cold coronaviruses and parainfluenza viruses, which cause upper and lower respiratory tract infections, have also dwindled to remarkably low levels this year, likely due to coronavirus-related precautions, such as masking, physical distancing, hand-washing and limited international travel.
But experts predict that this respite from seasonal viruses may leave us vulnerable, since fewer people will be exposed and gain immunity to the circulating strains.
"Susceptibility is increasing in the population," Shweta Bansal, a disease ecologist at Georgetown University in Washington, D.C., told The Atlantic.
For instance, children with no prior exposure to the viruses will be born, as usual, but fewer will encounter the viruses than would in an average year; meanwhile, the immunity in previously exposed adults will begin to wane. People with no or reduced immunity "are like fuel for the flu fire," Bansal said. "The more fuel is available, the easier it can be for an outbreak to happen."
The match may be struck as COVID-19 precautions lift, sparking a rebound in infections, Rachel Baker, an epidemiologist at Princeton University, told Science News. As the size of the susceptible population increases, "we need to be prepared for offseason outbreaks and potentially large outbreaks," Baker said.
For example, New South Wales in Australia usually sees RSV cases peak between April and June, but during the 2020 season, the number of positive RSV tests fell by more than 85% compared with recent years, Science News reported. But in late December, after COVID-19 restrictions in New South Wales lifted, RSV cases spiked; typically, only a few hundred cases are reported in late December, but in 2020, 6,000 positive RSV tests cropped up in just two weeks.
This Australian case "could be an interesting foreshadowing of what is to come in the Northern Hemisphere," Baker told Science News.
Scientists still don't know whether upcoming flu seasons will be bad, The Atlantic reported. But the lack of circulating flu strains does make it more difficult to prepare for the season. Scientists would normally track how different strains of the flu mutate through time, in order to forecast what versions of the virus might be prevalent in the upcoming season. This early sampling helps them to formulate new flu vaccines in advance.
But with so few flu cases to sample this year, scientists are short on data. The low level of circulation could theoretically snuff out certain strains of influenza, Florian Krammer, a virologist and flu expert at the Icahn School of Medicine at Mount Sinai, told The Atlantic. But on the other hand, brand new strains could emerge without scientists knowing about them, he said.
Originally published on Live Science