Scientists say that two common strains of the seasonal flu have seemingly vanished from circulation, likely due to public health measures like mask-wearing meant to slow the covid-19 pandemic. Though it will take time to confirm the disappearing act, the unexpected good news could make developing next season’s flu shot all the easier.
Every year, various types of the flu spread across the world, usually following a seasonal pattern of colder and/or drier weather. These flus are divided into two broad categories, A and B viruses, which are further divided into different groups. Both can mutate relatively quickly in a short amount of time, but influenza A viruses are the more dangerous variety, since they originally crossed over from animals like birds and can mutate enough to become the next source of a pandemic.
Scientists globally monitor the evolution of flu viruses by testing samples of confirmed flu cases from people who visit hospitals and doctors’ offices (the flu is always around, but it usually doesn’t cause major outbreaks until the typical season). This allows them to predict the likely batch of common strains that will circulate in the coming year and to then produce vaccines geared to provide immunity to those strains. This prediction process happens twice a year, accounting for the Northern and Southern hemisphere.
But since March 2020, we haven’t detected traces of two common flu strains: influenza B viruses belonging to the Yamagata lineage and a clade of the influenza A H3N2 virus, known as 3c3. So it’s possible, though not certain, that they may have gone extinct.
“Just because nobody saw it doesn’t mean it has disappeared completely, right? But it could,” Florian Krammer, a virologist and flu expert at Mount Sinai School of Medicine in New York, told STAT News.
What makes the theory more compelling is that the flu as a whole took a major break during the pandemic. Countries all over the world have reported significantly fewer cases of flu since early 2020. In the U.S. this winter, the flu essentially disappeared, causing only a single reported pediatric death (most seasons kill 100 to 200 kids). There are many reasons for this, but interventions like mask-wearing, higher rates of vaccination, and the physical closure of high-risk environments for flu spread, such as schools, are all thought to have played a part.
Of course, either flu virus may have survived in some segment of the human population, just not to the point of being detected. And even this brief respite from the flu won’t doom the virus forever. Influenza is still circulating in plenty of animal reservoirs, and as life in the U.S and other highly vaccinated countries gradually returns to normal, the opportunity for flu transmission between people will return as well. But the current situation could make predicting which strains will drive the next flu season a simpler task, NPR reports, since there will be less flu diversity out there to worry about. It’s even possible that future vaccines will only need to carry protection against three major strains of the virus, if the B/Yamagata lineage does remain gone, instead of the four-strain strategy now used.
Few things about this pandemic have been good, but a nearly nonexistent flu season and future, easier-to-handle flu seasons could be a silver lining.