As the fall faded Last year, some infectious disease researchers began to turn their attention away from the Covid-19 pandemic and back to something more familiar. This was the time of year when they usually started looking at their numbers for influenza, the seasonal flu – to see how bad the outbreak would be and to assess how well that year’s vaccine coped with the protein respiratory virus.
The answer was: bupkis. Hardly anyone was sick or died of the flu. A year earlier, during the 2019-2020 flu season – in fact 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 total 32,000 people died. But in the current season, the cases barely exceeded four figures. “There is always a vaccine season and a flu season. We’re used to working in that pattern, and the pattern has disappeared, ”said 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 control network. . “Now I am happy that I did not have to do Covid control and influenza control at the same time. That would have been a disaster. But at the same time it is this strange year. “
Strange indeed. And it’s not just the flu. Case numbers for respiratory syncytial virus, which primarily affects babies and, like flu, has a seasonal rhythm, has also bottomed out. According to a paper released last week, the missing list also includes enterovirus D68, a likely culprit behind the polio-like childhood disease acute flaccid myelitis. The virus and the AFM follow and go about every two years, and the last round in North America was in 2018. In 2020 they also missed their cue.
The why of it is not really a mystery. Probably. Most likely any masks, physical distance, hand washing, and other ‘non-pharmaceutical interventions’ that everyone – OK, almost everyone – to prevent the spread of Covid-19, did the kibosh on those other viruses as well. That’s not the only hypothesis, but it’s a good one.
The mystery is the how and what now. The answers can teach scientists more about how those other diseases infect humans and how to stop them. The mechanics of why those NPIs crushed at least three other respiratory viruses while Covid-19 was rampant is not clear. And even less clear is what a year without the flu means for the following winter and for the winters thereafter. Influenza kills 12,000 to 61,000 people in the US every year and is estimated to cost the economy $ 11 billion annually. For decades, even centuries, people have more or less accepted that risk. But if it turns out to be almost completely preventable, does people’s willingness to tolerate the risk change?
Pandemics happen when a virus hits its evolutionary groove. The virus that causes Covid-19 is called SARS-CoV-2, and when it declined in late 2019, no human immune system had ever seen it before. Nobody had any defense. The fact that people who had no symptoms could transmit it 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 takes only the slightest circumstance or genetic twist to turn a virus into a pandemic, the disease version of an arena-filling band, it doesn’t take much to limit a disease to the equivalent of playing from small clubs. “The Covid-19 controls – wearing a mask and social distancing – really work, and they work really well for other respiratory pathogens, too,” said Rachel Baker, an epidemiologist at Princeton University. Probably the main difference is that those other diseases have been happening for thousands of years and people are a little used to their charms. Even the flu, with its famous mutable genome requiring a new vaccine every year, leaves behind a measure of population-scale immunity. “With the seasonal illnesses, we have a lot of immunity to the population, we have vaccines and most people over 2 years old have had RSV,” says Baker. “That’s why you don’t have a seasonal pandemic.”