- In a
recent report, the Centers for Disease Control and Prevention (CDC) said that mitigation strategies to target SARS-CoV-2, the virus that causes COVID-19, could cause lower flu rates.
- All states in Australia varied in their shutdowns measures, but they all saw declines in flu as well as other respiratory viruses such as respiratory syncytial virus (RSV).
- The more severe the measures you take to limit human movement or contact, the more you will reduce respiratory infections, including flu and COVID-19.
The Southern Hemisphere’s flu season wasn’t as bad this year, probably due to pandemic-related shutdowns and public health interventions. Can the United States expect the same thing as we go into flu season?
“Based upon the very real decreased numbers in the Southern Hemisphere, it clearly appears that masking and social distancing will have a major impact on diminishing influenza illness in the United States this year,” noted Dr. Aaron Glatt, chief of infectious diseases and an epidemiologist at Mount Sinai South Nassau in Oceanside, New York.
The more severe the measures you take to limit human movement or contact, the more you will reduce respiratory infections due to COVID-19, influenza, RSV, and just about all infectious diseases, said Ian Barr, PhD, deputy director at the WHO Collaborating Centre for Reference and Research on Influenza (VIDRL). Barr is based in Australia.
Apart from SARS-CoV-2, the only other respiratory virus in Australia being seen is the one behind the common cold, he told Healthline.
Barr is expecting a low flu season in the United States.
“We know that high circulation of one respiratory virus tends to push out other respiratory viruses, known as viral interference, so this may also reduce influenza numbers,” he said.
Clues from the Southern Hemisphere
All states in Australia varied in their shutdowns measures, but they all saw declines in flu as well as other respiratory viruses and diseases such as RSV, metapneumovirus, and pneumococcal disease, Barr said.
In August 2019, which is typically Australia’s peak month for cases, there were 61,084 cases. In 2020, there were just 121 cases.
After SARS-CoV-2 started to circulate on a widespread basis last winter, indicators of flu activity declined in the Northern Hemisphere during its flu season.
As of now, the percentage of positive flu cases in the United States decreased from about 20 percent to 2.3 percent, according to the CDC.
U.S. labs saw a 61 percent decrease in the number of samples submitted from mid-September 2019 through the end of February 2020 — and a 98 percent decrease in flu activity. Summer flu circulation has been at a historic low in the United States.
That’s why experts are gleaning insights into how the flu behaved in the Southern Hemisphere, where the peak flu season — typically June through August — is fading off.
According to the World Health Organization FluNet platform, there was a lower flu prevalence from June through August of this year in Australia, Chile, and South Africa.
It’s possible that fewer flu cases were detected because people are avoiding doctor’s offices, which could result in fewer people getting tested, explained Dr. Ellen F. Foxman, an assistant professor at Yale School of Medicine.
“However, there seems to have been a decrease in both the number and the percentage of tests which have been flu-positive. This indicates that there has most likely been a real reduction in flu cases,” Foxman told Healthline.
Putting off the flu
As a result of COVID-19 mitigation measures along with flu vaccinations, experts say they’ll likely work to lower flu incidence. Some interventions could have a role in preventing the flu in the future, as well, but it’s unknown if current practices may just delay flu season, the CDC report pointed out.
“Initially, declines in influenza virus activity were attributed to decreased testing, because persons with respiratory symptoms were often preferentially referred for SARS-CoV-2 assessment and testing,” the CDC report stated. But ongoing efforts to test people for flu found little to no influenza virus.
If extensive community mitigation measures continue throughout the fall, flu activity in the United States “might remain low and the season might be blunted or delayed,” the report went on.
“Even though the goal of the social distancing measures has been to stop COVID-19, a side effect may be reducing transmission of other respiratory viruses including the flu,” Foxman noted.
Plus, we have a vaccine for the flu. Increased vaccination rates could lower the illnesses caused by the flu this year in the United States, too.
“The decrease in flu would only be expected to last as long as the efforts to prevent the spread of viruses last,” Foxman noted. “As social distancing measures ease, the protection against flu virus transmission would also be lost.”
“So this year, a lot of when and how respiratory viruses spread will be dependent on our actions as a society. Human behavior will be a much bigger factor than in other years since we usually do not go to such lengths to prevent the spread of respiratory viruses,” she continued.
As for whether a less active flu season could backfire, Barr said he’s not quite sure because it’s “uncharted territory.”
Influenza is a variable disease, meaning that some seasons aren’t as bad.
“It’s been unpredictable even without the advent of SARS-CoV-2,” he said. Factors can determine what will happen in the future, such as strains of flu active, vaccination rates, as well as interplay with SARS-CoV-2 circulation.
“Lower influenza seasons mean that fewer people are infected which does mean there will be more susceptible people in the subsequent year or years, so this might build up to a bigger influenza season the next year or next few years,” Barr added.
“I do not think having a less active flu season will backfire on us in any way,” Glatt said. “There is no evidence to suggest that we will have a delayed flu season if people mask and distance throughout the flu season.”
Jeffrey Shaman, PhD, a professor at the Columbia Mailman School of Public Health, said it’s hard to say what will happen this flu season with COVID-19 in play.
“If we’re coming out of the pandemic in March  and people return to more normal interactions, a spring flu outbreak is certainly possible,” he told Healthline.
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