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Public health officials and experts watching the dark cloud of the coronavirus pandemic have selected the smallest of the silver liners: this year’s flu transmission appears to be one of the lowest in recorded history.
Experts said it was too early to draw any conclusions on what the winter months might bring as colder weather descends in the northern hemisphere. But data from the southern hemisphere suggests the worst-case scenario – a wave of influenza piling up health systems already stressed by an outbreak of coronavirus cases – may not come true.
“They had incredibly low transmission rates,” Christine Petersen, an epidemiologist who studies influenza at the University of Iowa, said of the southern hemisphere. “There was no decent level of transmission anywhere except in Southeast Asia.”
Data collected by the World Health Organization shows remarkably low levels of influenza-like illness this year, compared to past years. In March – usually at the height of influenza season in the southern hemisphere – about 36 out of 1,000 ambulatory patients developed influenza-like illness. In spring 2017, the most recent year of significant spread, that number was north of 200 per 1,000 patients.
More recently, transmission rates have fallen even more.
“Globally, despite the continuation or even the increase in influenza testing in some countries, influenza activity has remained at levels below expectations for this time of year,” wrote the ‘WHO in early November.
In the United States, data collected by the Centers for Disease Control and Prevention (CDC) so far shows below-average influenza transmission. Only 1.5 percent of visits to a health care provider were for flu-like illnesses in the past week, the CDC’s FluView weekly report says.
Since September, 122,000 people have been tested for the flu, and only 319, less than 0.5%, have tested positive.
Experts said the low level of transmission was likely a combination of behavioral changes made during the coronavirus pandemic and some scientific luck – the two dominant flu vaccines developed this year both cover the particular type of flu that has circulated most widely, although data on the number of Americans who get their flu shots won’t be available until next year.
But the lion’s share of the credit goes to the behavioral changes people have made around the world – wearing masks, it turns out, reduces the spread of respiratory infections.
“We’ve all been somewhat silent about it, because it forces people to wear masks and then it doesn’t transmit, because it’s a respiratory disease,” Petersen said.
Health experts warn that there are still months of cold to come, a great opportunity for the flu to gain a foothold.
“People don’t travel as widely, so you may see the flu spreading slower than usual,” said Kelli Drenner, a public health expert at the University of Houston. “Thanksgiving, all bets are off. It will change. “
Low transmission rates are little reason for optimism at a time when the coronavirus is spreading faster than ever before, just before one or more COVID-19 vaccines hit the market.
“We could still be stupid,” Petersen said. Or, she added, “We might actually be seeing one of the lowest flu years ever.”
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