Remember the flu? The CDC and most epidemiologists agree that we are in “peak” flu season. By this time last year, almost 20 million Americans had contracted the Flu, ~200,000 had been hospitalized, and ~10,000 died, including ~100 children. In fact, in a typical year:

• Between 5% (~6,600,000) and 20% ( ~66,000,000) of American citizens contract the flu.

• ~250,000 Americans are hospitalized due to complications from the flu.

• ~35,000 Americans succumb to the flu.

This year is atypical. Though February usually marks the apex of the seasonal flu in America, remarkably, we have seen almost zero – you heard that correctly – close to zero documented influenza cases in the United States.

The Mayo Clinic conducted 20,000 flu tests between Dec 1st and Feb 1st, none came back positive. Of 800,000 samples tested by The Centers for Disease Control (CDC), just 1,500 were positive. Extrapolating these figures and applying them to a broad swath of America, in what is typically the most brutal time of year for influenza, just ~.02% of people are testing positive. Furthermore, thus far, just a few hundred people have been hospitalized and there has been only one documented fatality.

These figures are truly stunning, but are they surprising? Probably not.

Why?

The influenza virus shares some similarities to the coronavirus, including how it is communicated. According to the CDC, “People with flu can spread it to others up to about 6 feet away. Most experts think flu viruses spread mainly by droplets made when people with flu cough, sneeze or talk. These droplets can land in the mouths or noses of people who are nearby or possibly be inhaled into the lungs. Less often, a person might get flu by touching a surface or object that has flu virus on it and then touching their own mouth, nose, or possibly their eyes.” Sound familiar? Of course, it does. This is synonymous to how COVID-19, and other variants of the virulent coronavirus, are transmitted.

Before COVID-19 reared its ugly head, very few people wore masks in public, washed their hands as often (admit it, you did not), self-quarantined when symptomatic, feeling sick, or even just exposed to a sick person, or practiced social distancing (unless you were at one of my family gatherings). Furthermore, it was less socially frowned upon to come to the office or join a group for a meal when feeling ill. It would be shall we say, “ill-advised,” on several levels to try that now.

These and other changes in behavior - either voluntarily taken by some, or mandatorily enforced upon others - to contain the spread of COVID-19, has rendered the flu almost non-existent this season.

This then begs the question: Why is the flu practically non-existent but COVID-19 still extremely prevalent, to the tune of ~10,000 new cases per day despite a pickup in inoculations? The answer is that although the two viruses are spread in similar ways, COVID-19 is more contagious than the flu.

Epidemiologists measure how contagious a disease is using something called the R0 or the R Factor. The granularity underpinning R0 calculations go well beyond the scope of this post. That said, the higher the R0, the more transmittable a virus is. When R0 drops < 1, a disease ceases to spread.

A typical seasonal flu carries a R0 of between 1 and 2 (R1-R2). COVID-19’s R0 is believed to be between 2 and 3. Human behavioral changes (and the beginning of a world-wide inoculation program) have driven the R0 of COVID-19 down, to somewhere likely between 1-2. Those same changes appear to have driven the R0 for the flu < 1, thus virtually rendering it non-existent this season.

A Silver Lining…

The precipitous drop in influenza cases this season has been a silver lining for hospitals, urgent care clinics, and the dedicated healthcare workers who staff them. Indeed, the dearth of flu patients has freed up much-needed bedspace for COVID patients. Thank goodness for that. At COVID’s recent peak in early January, hospitals were operating at over 100% of capacity in some instances. Had the flow of flu patients been “normal,” some hospitals might have been forced to ration care.

…Or Not?

Minimal flu this year might ironically sow the seeds of a deadly flu season in the future. For one, scientists will have a more difficult time tracking mutations and hence tailoring an effective seasonal flu vaccine. Second, a lack of exposure in the present makes people more vulnerable in the future. To help develop a level of immunity to a virus, one must paradoxically be exposed to that virus. Less exposure often translates into a more deadly case if a person becomes infected later. This issue is particularly acute for children; their bodies have had less exposure to different variants of the flu.

Flu Vaccine

The mortality rate for influenza in the United States is about one death per 1,000 instances or .1%; low but certainly not nil.

Even though a flu vaccine exists, over 50% of American’s decline inoculations. A commonly stated reason why is the misplaced fear that the flu vaccine can cause the virus. This is categorically untrue and medically impossible.

The flu vaccine is prepared months before the onset of flu season. Sometimes there is a “mismatch” between the vaccine and which strain of the flu happens to be most prevalent in a given year. However, it is indisputable that regardless of what type of strain happens to present itself most often, the flu vaccine helps, at least at the margins.

If you have not already done so, roll up your sleeve and tell your healthcare provider that you would like a flu shot.