As autumn faded Last winter, several infectious disease researchers began to turn their attention away from the Covid-19 pandemic and return to something more familiar. This was the time of year when they usually started looking at their flu count, seasonal flu – to see how bad the outbreak would be and to assess how well the respiratory protein vaccine had done that year.
The answer was: bupkis. Almost no one was ill or dying of the flu. A year earlier, during the 2019-20 flu season – practically in the fall and winter, peaking in December, January and February – 18 million people in the US saw a doctor for their symptoms, and 400,000 had to be hospitalized. In all, 32,000 people died. But this season, cases have barely gone over four digits. “There is always the vaccine season and the flu season. We are used to working on this model, and the model has disappeared, ”says Emily Martin, an epidemiologist at the University of Michigan School of Public Health who is part of the Centers for Disease Control and Prevention’s flu monitoring network. “Now, I’m glad I didn’t have to control Covid and the flu at the same time. It would have been a disaster. But at the same time, it’s a strange year. ”
Strange indeed. And it’s not just the flu. The numbers of cases for respiratory syncytial virus, which primarily affects children and, like the flu, also has a seasonal rhythm at the bottom. According to a paper that appeared last week, the missing-in-action list also includes enterovirus D68, a probable culprit behind polio, similar to acute flaccid myelitis. The virus and AFM come and go on a cycle of about two years, and the last round in North America was in 2018. In 2020, they, too, lost their mark.
Why it’s not really a mystery. Probable. Most likely, all the wearing of the mask, physical distance, hand washing and other “non-pharmaceutical interventions” that everyone – OK, close everyone – did to prevent the spread of Covid-19, also put kibosh on other viruses. This is not the only hypothesis, but it is a good one.
The mystery is How and what’s next. The answers could teach scientists more about how these other diseases infect people and how to stop them. The mechanism of why these NPIs crushed at least three other respiratory viruses while Covid-19 did not is clear. And even less clear is what the flu-free year will mean for next winter and after 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 an estimate. For decades, even centuries, people have accepted this risk. But if it turns out to be almost entirely preventable, will people’s desire to tolerate risk change as well?
Pandemics happen when a virus hits its evolutionary ditch. The virus that causes Covid-19 is called SARS-CoV-2, and when it fell at the end of 2019, no human immune system has seen it before. No one had a defense. The fact that people who had no symptoms could transmit it made it different from most of its cousins respiratory pathogens – different enough to take advantage of human social interactions and become global.
But, as it takes only the slightest circumstance or a genetic twist to turn a virus into a pandemic, the disease version of an arena filler strip, it doesn’t take much to limit a disease to the equivalent. small club game. “The Covid-19 control measures – wearing a mask and social distancing – really work and work very well for other respiratory pathogens,” says Rachel Baker, an epidemiologist at Princeton University. The essential difference is probably that those other diseases have been playing concerts for thousands of years, and people are a little excited about their charms. Even the flu, with its famous modifiable genome, which requires a new vaccine every year, leaves behind a certain level of population-wide immunity. “With seasonal diseases, we have a very high 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.”