Friday, June 2, 2023

Covid-19 meant a year without the flu. It’s not all good news

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As the fall faded for the winter of last year, a few infectious disease researchers began to divert their attention from the Covid-19 pandemic to something more familiar. This was the time of year they usually started looking at their numbers for the flu, the seasonal flu – to see how severe the outbreak would be and to gauge how well this year’s vaccine treated the virus. protean respiratory.

The answer was: the bupkis. Almost no one was sick or dying of the flu. A year earlier, during the 2019-20 flu season – mostly fall and winter, peaking in December, January and February – 18 million people in the United States saw a doctor for their symptoms and 400,000 had to be hospitalized . A total of 32,000 people died. But in the current season, the cases barely crossed four digits. “There is always a vaccination season and an influenza season. We’re used to working with that model, and the model is gone, ”says Emily Martin, an epidemiologist at the University of Michigan School of Public Health who is part of the Centers for Disease Control’s influenza surveillance network. and Prevention. “Now I’m glad I didn’t have to do the Covid check and the flu check at the same time. It would have been a disaster. But at the same time, it’s this strange year.

Strange indeed. And it’s not just the flu. The number of cases for respiratory syncytial virus, which primarily affects babies and, like the flu, has a seasonal pattern, has also hit a low. According to a paper released last week, the list of missing people in action also includes enterovirus D68, possibly responsible for the acute flaccid myelitis of the polio-like illness of children. The virus and AFM come and go on a cycle roughly every two years, and the last cycle in North America was in 2018. In 2020, they too missed their signal.

The Why it’s not really a mystery. Probably. Most likely, all of the mask-wearing, physical distancing, hand washing, and other “non-pharmaceutical interventions” that everyone else – OK, almost everyone – did to prevent the spread of Covid-19 also put the kibosh on these other viruses. This is not the only assumption, but it is a good one.

The mystery is the How? ‘Or’ What and the sequel. The answers could teach scientists more about how these other diseases infect people and how to stop them. It is unclear why these NPIs crushed at least three other respiratory viruses as Covid-19 spread. And even less clear is what a flu-free year will mean for next winter, and for subsequent winters. The flu kills between 12,000 and 61,000 people in the United States each year and costs the economy $ 11 billion annually, according to one estimate. For decades, even centuries, people have simply accepted this risk. But if it turns out to be almost entirely preventable, will people’s willingness to tolerate the risk change as well?

Pandemics occur when a virus hits his evolutionary groove. The virus that causes Covid-19 is called SARS-CoV-2, and when it fell in late 2019, no human immune system had ever seen it before. No one had a defense. The fact that people who had no symptoms could pass it on made it different from most of its respiratory pathogenic cousins ​​- just different enough to take advantage of human social interactions and go global.

But just as it only takes the slightest circumstance or genetic twist to turn a virus into a pandemic, the disease version of a group that fills the arena, neither does it take to limit a disease to the equivalent to playing in small clubs. “The Covid-19 control measures – mask wearing and social distancing – really work, and they work very well for other respiratory pathogens as well,” says Rachel Baker, an epidemiologist at Princeton University. The main difference is probably that these other diseases have been playing concerts for thousands of years, and humans are somewhat used to their charms. Even the flu, with its reputedly mutable genome that requires a new vaccine every year, leaves behind a certain level of population-wide immunity. “With seasonal illnesses, we have great population immunity, we have vaccines, and most people over the age of 2 have had RSV,” says Baker. “That’s why you don’t have a seasonal pandemic.”


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