On February 24, 2020, the first documented U.S. case of community transmission of Covid-19 was reported from a specimen collected by the Seattle Flu Study. The Seattle Flu Study was designed as a surveillance of persons reporting respiratory symptoms. In a normal year it detects high rates of influenza, particularly during winter months—most years, influenza sickens hundreds of thousands of Americans and kills 30-50,000. But this has been anything but a normal year. Even as the surveillance system has been picking up Covid-19 cases, of the thousands of nasal swabs the research team has analyzed, an extraordinarily low number have tested positive for influenza.
Covid-19, like influenza, is a virus that moves through the air. We might have expected that with so much Covid-19 around, flu would be a fellow traveler, likewise infecting millions of Americans. But the only virus that’s had a successfully infectious year in 2020 was the new Covid-19. Other respiratory viruses have been rarer this season too, such as respiratory syncytial virus, parainfluenza, and even other coronaviruses that cause common colds. It’s not easy to find people with the coughs, running noses and fevers, typical this time of year, who are not singularly infected with Covid-19.
Why? Perhaps the behavioral changes triggered by Covid-19—masking, washing hands, physical distancing—have made a difference. With businesses and offices shut, with sick leaves taken more seriously, with schools and daycare sites closed, with an immobilized population, there’s less social interaction. Influenza vaccination rates across the country are a bit higher, but that’s probably not enough to explain the drop in what has been historically our most lethal infectious disease. This suggests that Covid-19 is really far easier to catch than these other more common respiratory illnesses.
What have we learned then during this year of the respiratory virus? Public health measures work, not only for Covid-19, but also for influenza and other common respiratory illnesses. Second, surveillance, one of the core activities of public health, works. Influenza surveillance centers already exist around the globe, and along with local studies like the one in Seattle, are now scouting for Covid-19 as it enters its second year among humans. Third, new vaccine technologies will matter when influenza recurs. In the past, flu vaccines took half a year to develop and manufacture; the RNA-based Covid-19 shots are easier and faster to update and may make us nimbler in adjusting vaccine ingredients to novel influenza strains that arise and which we need protection from. Can we embed these lessons in our approach to respiratory disease going forward? If we did, this may be one of the positive legacies of this Covid-19 moment.
Michael Stein & Sandro Galea
As we re-emerge from the pandemic, 2021 stands to be a turning point year for public health. In The Turning Point’s weekly essays, we reflect on what we learned during 2020, and what we are learning during 2021, that can guide us to the creation of a better, healthier world.