Where did the flu go? Influenza activity has not been so low in recent memory, and COVID has had a lot to do with it

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Amid a pandemic that has literally reconfigured the daily lives of most of the planet, Massachusetts and the country are experiencing the quietest flu season in years, with virtually no hospitalizations for flu reported at some of the larger hospitals. of State.

“We haven’t seen any influenza at (UMass Medical Center), which is very unusual at this time of year,” said Dr. Robert Finberg, infectious disease expert at UMass Medical School.

At the end of January, about 0.05% of hospitalizations statewide were associated with influenza, with about 0.77% of health care visits related to seasonal respiratory infection. Around the same time last year, visits for influenza were in the range of 5 to 6%, and over 3% in 2018, according to data compiled by the Massachusetts Department of Public Health.

Nationally, just 0.1% of respiratory samples tested positive for influenza in clinical labs during the last week of January, data showed. Between October 1 and January 30, only 155 people were hospitalized with the flu, according to the Centers for Disease Control and Prevention.

Dr David Hooper, chief of the infection control unit at Massachusetts General Hospital, said he didn’t think the state’s largest hospital had treated anyone for the flu this season. He attributes the state’s aggressive vaccination campaign ahead of fears that the the autumn and winter months would bring a “twindemia” of COVID and cases of influenza.

“I’ve been in this business for many years and have never seen it this low,” Hooper said.

The Ministry of Public Health required that all children 6 years of age and over who are studying up to college or daycare get the flu shot to ease the burden on hospitals as winter approaches. Officials have since waived the mandate because the flu season seemed to be milder than usual.

But few expected it to be so quiet, experts say. Although there is an annual ebb and flow in the severity of influenza transmission related to the rate of viral mutation (influenza tends to mutate at a much higher rate than COVID) and the degree of Immunity after a particularly active year, “-disease” in Massachusetts and across the country remains well below baseline – an indication that something else could go beyond seasonally.

With all eyes on COVID trends, the fact that the flu appears to be at its lowest point in years is good news and a testament to the effectiveness of new health and safety protocols – masking, social distancing – to ward off other infectious diseases. diseases, say experts.

“That’s the only explanation,” said Dr. Christopher Gill, an infectious disease physician and faculty member in the Department of Global Health at Boston University. “What we are doing to prevent the person-to-person spread of COVID will protect us from any disease that spreads through the respiratory tract. “

Influenza infections have remained consistently high during the 2019-20 season, which saw two different strains spread to the United States. Influenza activity remained exceptionally high, even as the COVID pandemic began to take hold.

Flu season comparison.

Without the widespread COVID testing infrastructure in place to properly diagnose sick patients, Gill says it is possible that some of the ILI cases reported during the 2019-2020 season were in fact the result of coronavirus infections. , not the flu.

There are other theories to help explain the flu’s near disappearance this season. Since influenza viruses mutate so frequently, essentially creating new viruses – a process called antigenic drift and displacement – the degree of immunity of the population varies, and in tandem with genetic changes.

“If there’s a big year when the flu virus has changed a lot, then people will build up antibodies, followed by fewer infections afterwards,” Finberg said.

But if the opposite happens and the virus remains relatively fixed in nature, immunity against a previous outbreak can help guard against a resurgence of that same or similar strain of influenza.

“A lot of people attribute the lack of flu this year to masking and social distancing,” Finberg said, “but I don’t think that explains it all.”

While there appears to be some consensus that COVID will not just go away when enough people receive the vaccine, experts say there could be important lessons from examining the impact of masking and distancing social, as well as other government-imposed restrictions on other airways. -diseases transmitted such as influenza.

But, they warn, flu season is still underway and cases could increase if people let their guard down.

“Obviously, nature has the last word,” Hooper said.

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