AILSA CHANG, HOST:
The flu is a seasonal illness. Flu infections peak in the winter. Well, winter is coming to an end in the Southern Hemisphere, and people there have just gone through a strange flu season, one deeply affected by the COVID-19 pandemic. NPR's Nell Greenfieldboyce reports that their experience may be a sign of what's to come in northern countries like the U.S.
NELL GREENFIELDBOYCE, BYLINE: When the virus that causes COVID-19 started spreading widely in February and March, public health officials in the Southern Hemisphere realized they were about to face a double whammy. Their flu season starts in May or June. There's always deaths and hospitalizations from flu. And now here was another severe respiratory virus.
SYLVAIN ALDIGHIERI: The countries took it very, very seriously.
GREENFIELDBOYCE: Sylvain Aldighieri is the incident manager for COVID-19 with the Pan American Health Organization. He says Southern countries did all they could to prepare for flu.
ALDIGHIERI: They bought more vaccine. They vaccinated more people during the pre-flu season.
GREENFIELDBOYCE: Then they waited for influenza cases to start rising. They waited and waited and waited.
ALDIGHIERI: Now we are well-advanced during the flu season in the South. And we have not seen any spike, any upsurge of flu.
GREENFIELDBOYCE: Flu hasn't totally disappeared, but it's way, way down. For example, take one three-week period in the middle of winter in Chile. He says over 3,000 patients with flu-like symptoms were tested.
ALDIGHIERI: And zero test were positive for influenza.
GREENFIELDBOYCE: Hundreds of those tests would normally be positive for flu. The same pattern is being seen in southern Africa, Australia. Kanta Subbarao directs the World Health Organization's Collaborating Centre for Reference and Research on Influenza in Melbourne.
KANTA SUBBARAO: We are totally surprised. I mean, we had influenza activity in January and February, and we have a few isolates from March. And then it just totally dropped off.
GREENFIELDBOYCE: So why did this happen? No one is really sure, but everything being done to stop COVID-19 is surely hitting flu as well.
SUBBARAO: So the restriction on travel is a big, big element - mask-wearing, hand-washing and all the social distancing.
GREENFIELDBOYCE: Still, she says the northern parts of the world should not be complacent and think they're off the hook for flu.
SUBBARAO: Because influenza surprises us. Viruses surprise us. We're sort of seeing very little influenza activity in the Southern Hemisphere. But that doesn't allow me to predict that that will be the case for the Northern Hemisphere.
GREENFIELDBOYCE: She and other flu experts say, get vaccinated.
STACEY SCHULTZ-CHERRY: This is one of those years that it's more important than ever to get your flu vaccine.
GREENFIELDBOYCE: Stacey Schultz-Cherry is a flu researcher at St. Jude Children's Research Hospital in Memphis, Tenn. She says scientists always look at what flu strains are circulating to make predictions about what should go into next year's flu vaccine. And even though flu cases are oddly low, they'll still be able to do that.
SCHULTZ-CHERRY: I think if it had disappeared completely, we'd be in a very different ballgame. But it hasn't. There's still flu out there.
GREENFIELDBOYCE: The fact that flu is still out there, however, is why she personally remains worried about what will happen in the U.S. and the rest of the Northern Hemisphere when its flu season starts later this year.
Nell Greenfieldboyce, NPR News.
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