Countries in the Southern Hemisphere are reporting lower numbers of flu cases this year compared with previous years—and health officials are attributing the decline to widespread coronavirus restrictions such as mask wearing, travel restrictions, and social distancing.

The 2019-2020 flu season has come to an end. See it, charted.

US braces for 'one of the most difficult times … in American public health'

As new coronavirus cases continue to surge in America, U.S. hospitals are bracing themselves for a huge wave of seriously ill flu and coronavirus patients in the upcoming fall and winter months.

Between the start of flu season and the United States' usual cold weather pushing everyone inside, CDC Director Robert Redfield has said "the fall and winter of 2020 and 2021 are going to be probably one of the most difficult times that we've experienced in American public health."

Cases of the flu drop in the Southern Hemisphere

But in the Southern Hemisphere—where winter began to descend nearly two months ago—the annual influx of flu and respiratory virus patients "never came," the Wall Street Journal's David Luhnow and Alice Uribe report.

According to Luhnow and Uribe, Chile has recorded 1,134 seasonal respiratory infections so far this year, compared with 20,949 such infections during over the same time period last year. And in the first two weeks of July, which typically is the height of flu season in the Southern Hemisphere, Chile reported no new cases of the flu.

Claudia Cortés, a doctor in Chile, said although physicians "keep checking for the other viruses … all we're seeing is [Covid-19]." She added, "We were surprised by the decline in the other viruses like influenza. We never dreamed it would practically disappear."

Similarly, in Brazil, even though the country has seen a large number of coronavirus-related deaths, officials reported 2,085 hospitalized flu patients in week 27 of the country's flu season, which is down significantly from the 3,445 hospitalized flu patients the country reported during the same week last year.

The number of lab-confirmed cases of the flu also plummeted by 64% in Argentina, Luhnow and Uribe  report, dropping from 420,737 between January and June of 2019 to 151,189 cases in the same time frame this year.

South Africa also has reported startling declines, with doctors saying there haven't been a sufficient number of flu cases to even report that the seasonal epidemic happened. And in Australia, the country's National Notifiable Diseases Surveillance System recorded only 85 new laboratory-confirmed cases of influenza in the last two weeks of June—a stark difference from the 22,047 confirmed cases recorded during the same time last year.

"This [decline] surprised me," Sylvain Aldighieri, deputy director of the Department of Health Emergencies at the Pan American Health Organization, said. "We were expecting a double burden of cases, because in countries like Chile and Argentina, the flu winter epidemic places a high burden on health care services."

Experts credit stringent coronavirus restrictions

According to Aldighieri, influenza likely would have resulted in the same numbers of hospitalizations and deaths this year as in previous years had it not been for strict coronavirus-related restrictions that some countries have in place.

For instance, a lot of countries in the Southern Hemisphere—such as Argentina, New Zealand, and South Africa—had implemented strict lockdowns. And in Australia, the majority of stores are still closed.

Richard Medlicott, a general practitioner in New Zealand, said he believes school closures prevented the spread of flu, and that could be part of the reason his clinic experienced a 90% decline in flu patients and a 60% decline in other respiratory illnesses so far in 2020 when compared with last year.

"Children are the main reservoir [of these viruses]," Medlicott said. "They haven't been at child care and that has meant they've had less chance to spread it in the community."

Restrictions on incoming air travel during the Northern Hemisphere's flu season also helped prevent travelers from bringing the flu to the Southern Hemisphere. According to Luhnow and Uribe, Argentina, Australia, Chile, and New Zealand shut down international arrivals in March.

"Strict border restrictions and alert-level-based response including social distancing measures has had an impact," said Sarah Jefferies, a public-health physician at New Zealand's Institute of Environmental Science and Research.

And there are other habits, such as hand washing and mask-wearing, that are catching on in the Southern Hemisphere that help prevent the spread of influenza as well as the novel coronavirus, Medlicott said. In addition, increased vaccination rates for the flu in countries such as Australia and Chile have helped to curb influenza's spread, especially among older and high-risk residents who are now more likely to seek out the vaccines. There's also been an increased use of telemedicine, which means patients can contact providers without visiting doctors' offices or hospitals, where germs are more common.

If those behaviors are sustained, flu rates could continue to decline for many years, Medlicott said.

Could this happen in the US?

Still, Aldighieri said the United States and Europe should consider preparing for their typical flu seasons.

Aldighieri pointed out that, unlike the strict restrictions on international travel in the Southern Hemisphere, the United States and Europe have not imposed nearly so stringent international travel restrictions, which means they are more likely to receive international visitors carrying the flu.

And in the United States, according to Luhnow and Uribe, mask wearing is still viewed as controversial and vaccination rates are at a record low. In addition, a lot of states are in the process of loosening coronavirus-related restrictions and reopening nonessential businesses and schools.

And doctors in the Southern Hemisphere say influenza's danger hasn't cleared on their end, either. They pointed out that there are still a few months left in their flu season, meaning an increase in cases could hit soon, especially if people stop social distancing and wearing masks, Luhnow and Uribe report (Lunhow/Uribe, Wall Street Journal, 6/22).