As the autumn disappeared by the winter of last year, some infectious disease researchers began to divert their attention from the Covid-19 pandemic and return to something more familiar. This was the time of year when they usually started looking at the flu numbers, the seasonal flu – to see how bad the outbreak would be and to assess how well that year’s vaccine handled the multiform respiratory virus.
The answer was: bupkis. Almost no one was sick or dying from the flu. A year earlier, during the 2019-20 flu season – basically fall and winter, peaking in December, January and February – 18 million people in the United States went to a doctor to check their symptoms and 400,000 had to be hospitalized. Overall, 32,000 people died. But in the current season, the cases have barely exceeded four digits. “There is always a season of vaccines and flu. We are used to working on that standard, and the standard is gone, ”says Emily Martin, an epidemiologist at the University of Michigan School of Public Health who is part of the flu monitoring network at the Center for Disease Control and Prevention. “Now, I’m happy that I don’t have to do Covid and flu control at the same time. This would have been a disaster. But at the same time, it’s a strange year. “
Really weird. And it’s not just the flu. The case numbers of the respiratory syncytial virus, which mainly affects babies and, like the flu, has a seasonal rhythm, have also hit rock bottom. According to an article published last week, the list of missing persons in action also includes enterovirus D68, a probable culprit behind acute flaccid myelitis, a polio-like disease in children. The virus and AFM come and go in a cycle of approximately every two years, and the last round in North America was in 2018. In 2020, they also lost their cue.
THE why of this is not really a mystery. Probably. Most likely, all mask use, physical distance, hand washing and other “non-pharmaceutical interventions” that everyone – OK, almost everyone – did it to prevent the spread of Covid-19 also killed those other viruses. This is not the only hypothesis, but it is a good one.
The mystery is the how and what comes next. The answers can teach scientists more about how these other diseases infect people and how to prevent them. The mechanics of why these NPIs destroyed at least three other respiratory viruses while Covid-19 was running wild is not clear. And even less clear is what a flu-free year will mean for the coming winter, and for later winters. The flu kills 12,000 to 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 simply accepted that risk. But if it turns out that it is almost entirely preventable, will people’s willingness to tolerate risk also change?
Pandemics happen when a virus reaches its 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 seen it before. No one had any defenses. The fact that people without any symptoms could transmit it made him different from most of his respiratory pathogen cousins - just different enough to take advantage of human social interactions and go global.
But just as it takes only the smallest circumstance or genetic turnaround to turn a virus into a pandemic, a band’s version of the disease to fill the arena, it doesn’t take much to limit a disease to the equivalent of playing in small clubs. “Covid-19’s control measures – wearing a mask and social detachment – really work, and work very well for other respiratory pathogens too,” says Rachel Baker, an epidemiologist at Princeton University. The main difference is probably that these other diseases have been around for thousands of years and humans are a little used to their charms. Even the flu, with its famous mutable genome that requires a new vaccine each year, leaves some level of immunity on a population scale behind. “With seasonal diseases, we have a lot of population immunity, we have vaccines and most people over 2 years old had RSV,” says Baker. “That’s why you don’t have a seasonal pandemic.”