INDIANAPOLIS — The 2020-21 flu season will go down as one of the mildest in recent history, although not necessarily the mildest ever.
Flu activity in Indiana never rose above “low” levels and the state recorded just five deaths attributable to flu, well below the typical annual average.
That trend wasn’t just seen in Indiana but nationwide as health officials contribute a year of public health precautions linked to stemming the spread of COVID-19 as a main driver for severely suppressing flu activity.
Going into this flu season there were expectations of a very mild impact after southern hemisphere nations, which have their winter during the north’s summer months, had minor flu impact during the initial onset of the COVID-19 pandemic in mid-2020.
In the final week of flu surveillance in Indiana, the state once again recorded “minimal” flu activity, with 557 new instances of “influenza-like illness” logged at surveillance sites across the state. That brings the 2020-21 total to 15,881 instances.
The percentage of cases seen at outpatient facilities was down slightly to 1.05% in the final week from 1.18% the week before.
The percentage of cases reported from urgent care centers and emergency rooms also dipped to 1.01% from 1.04% in the final week.
Both figures are typical for this time of year as flu activity usually recedes as warmer weather sets in during spring.
Looking back on the 2020-21 season as a whole, however, this flu season was one of the mildest the state has seen ever.
Although numbers crept up a little in November and December, the state never exceeded a rate of 2% flu reports.
Indiana spent almost all of the season in “minimal” spread, the lowest rating, outside of a few short weeks at “low,” the second-lowest level.
While flu numbers typically start to shoot up in November/December and stay elevated sometimes through late March, that never happened in 2020-21 as activity remained mostly flat throughout the more than 30 weeks of surveillance.
The biggest reasons why, according to health officials?
Masks, social distancing and improved hygiene practices helped keep down flu, which is also spread via respiratory droplets just like COVID-19.
While COVID-19 still saw widespread transmission even with those precautions in place — especially during a late 2020 surge that started in October and persisted before peaking in mid-December — analysis has shown the novel coronavirus to be generally more infectious than a typical flu strain.
“While COVID-19 and flu viruses are thought to spread in similar ways, COVID-19 is more contagious among certain populations and age groups than flu. Also, COVID-19 has been observed to have more superspreading events than flu. This means the virus that causes COVID-19 can quickly and easily spread to a lot of people and result in continuous spreading among people as time progresses,” the Centers for Disease Control and Prevention notes on its flu vs. COVID-19 information page.
It’s possible that focus on flu may have been less this year than in other non-pandemic years, thus leading to reduced surveillance, but as COVID-19 has its own confirmatory test it’s unlikely that flu cases were wrongly being classified as coronavirus.
Since flu surveillance also tracks “influenza-like” illness without requiring a specific test for flu, the definition is more broad to capture symptomatic people even if they don’t have a confirmatory test for a particular flu strain.
Coupled with low flu rates recorded through the season, the Indiana State Department of Health recorded just five deaths attributable to influenza this year, which is far lower than most seasons.
Over the prior five years, the state was averaging about 150 flu deaths per year, which is skewed slightly upward by an unusually harsh 2017-18 flu season that had 336 flu deaths.
Outside of that high outlier 2017-18 season, Indiana typically has about 70-150 flu deaths per year, so having just five this season is an extreme outlier to the low end.
COVID-19 has been accountable for more than 13,000 deaths in Indiana since March 2020, for comparison.
That being said, five deaths from flu isn’t the lowest number in recent Indiana history.
The 2011-2012 season was also an unusually mild year, in which Indiana recorded just three deaths from flu that season, according to end-year reports posted to the Indiana State Department of Health website.
“In comparison to other seasons, the 2011-2012 season set a new record for the lowest and shortest peak of influenza-like illness,” the Centers for Disease Control and Prevention wrote in its recap of that season. “The season began late and was mild compared to most previous seasons for which surveillance data is available.”
The impacts of flu this year, nationally, are even more minor than that low year, the CDC reports, as hospitalization rates for flu sit at just 0.8 people per 100,000.
“This is lower than rates for any season since routine data collection began in 2005, including the low severity 2011-12 season,” the CDC reported. “The end-of-season rate is one-tenth the rate as during the 2011-12 season.”
Nationally, the CDC has also recorded just one pediatric death from flu this entire season, where typically around 200 are normal in previous years.