Influenza, usually raging throughout the Northern Hemisphere this time of year, has become virtually invisible.
It is a small bright spot amid Covid-19, although the number of people saved from a flu death pales next to the number dying from the new pandemic. It also presents questions that doctors around the globe will likely be wrestling with for years: If flu can be nearly wiped out this season, why not every season? Which steps help the most to stop the flu from spreading?
“This is an extremely puzzling phenomenon. We’re in a historic, unbelievable situation,” said Norio Sugaya, a pediatrician who serves on a World Health Organization influenza committee.
The WHO says the measures people and governments are taking to prevent the spread of Covid-19, such as wearing masks and limiting public gatherings, have probably helped keep the flu in check. Increased flu vaccination rates may also be contributing, it says.
Another hypothesis holds that the broad spread of SARS-CoV-2, the virus that causes Covid-19, in countries like the U.S. may play a role in blocking the flu by lifting people’s immunity against other viruses. One study in the spring of 2020 in New York City found that people testing positive for SARS-CoV-2 were far less likely to be carrying other common viruses such as influenza viruses. Still, research into that hypothesis is just beginning.