5 Reasons Flu Cases Are Way Down This Year

‘I don’t want to jinx us, but this may turn out to be the mildest flu season on record’

A portrait of a young woman wile wearing a face mask for protection from cold and flu and viruses.
A portrait of a young woman wile wearing a face mask for protection from cold and flu and viruses.
Photo: recep-bg/E+/Getty Images

It’s nearly halfway through the 2020–2021 flu season, and as I walk the halls of the hospital where I work, I realize none of the patients are here with influenza. In fact, only 925 cases of flu have been confirmed in the United States thus far this season, and none in my home state of Montana. This compares to 63,975 confirmed cases in the United States at the same time last year.

It’s important to note that the true number of flu cases is always larger than the number reported, because many individuals with flu symptoms do not seek testing. The CDC uses the number of confirmed cases to estimate the number of true cases that occur in a given season. In what was considered a moderate 2019–2020 flu season, the CDC estimated a total of 47.5 million cases occurred. Because the number of confirmed cases thus far has been so historically low, the CDC has not yet published an estimate for the total number of cases this season.

Because the flu virus is significantly less contagious than the novel coronavirus, gains from masking are even more pronounced when it comes to influenza.

Remember when experts were worried about what might happen if Covid-19 cases surged at the same time flu season ramped up? Here’s what Dr. Anthony Fauci said about that on August 12, 2020: “We haven’t had a situation with this kind of potential, where we might have two illnesses, one that is of epidemic proportions and the other pandemic, co-circulating at the same time.”

I don’t want to jinx us, but this may turn out to be the mildest flu season on record. It’s a good thing, too, because the coronavirus has given us all we can handle. But aren’t you a little curious about what happened to the flu? Let’s look at the five best explanations as to where it went.

Increased flu vaccinations

By December 2020, the CDC estimated that 53% to 54% of adults in the United States had received the seasonal influenza vaccine. This was up from 42% in December 2019. The frequency of flu vaccinations has increased in other countries, too. For example, Australia dramatically increased its number of recipients, from 4.5 million in the 2019 season to 7.3 million in 2020.

Every year, some of my patients complain about the flu vaccine’s low level of effectiveness, and every year I explain that the vaccine would be more effective if more people chose to get it. While the vaccine isn’t the only reason for low flu activity this year, I am hopeful that the positive effects of vaccination observed this season will ultimately translate to more doses being administered in future years.

Masks

As more studies are conducted, scientific evidence continues to suggest that multiple types of masks, including cloth face masks, can reduce the spread of Covid-19. This fits with what has already been demonstrated in multiple randomized controlled trials highlighting the effectiveness of masks to slow the spread of influenza.

Because the flu virus is significantly less contagious than the novel coronavirus, gains from masking are even more pronounced when it comes to influenza. For example, without masking or other mitigation measures, some scientists estimate each patient with Covid-19 passes the virus on to another 2.4 people. Others estimate this number to be even higher. This is called the reproductive number, or R₀. For influenza, the R₀ is lower — about 1.4, depending on the season. It’s estimated that masks reduce the R₀ of Covid-19 to 1.35, and although not proven, it’s well within reason to think masks could reduce the R₀ of influenza to less than one. This is an important threshold, because if a person with influenza wearing a mask spreads infection to an average of less than one person, then viral transmission among a population begins to decline.

Viral competition

Although data is lacking that specifically shows the novel coronavirus, SARS-CoV-2, preventing an influenza infection, studies with other respiratory viruses suggest viral competition does take place. For instance, patients with rhinovirus infections have been shown to be less susceptible to infection with common-cold coronaviruses. Some experts suspect viral competition may indeed be occurring as a result of the pandemic. The presumption being that patients ill from Covid-19 may be less susceptible to influenza — perhaps because of their heightened immune response or because SARS-CoV-2 manages to outcompete the influenza virus in a race to invade cells of the respiratory tract.

Social distancing

We’ve seen it all too many times during the pandemic: A person coughing in public followed by piercing glares of instant judgment beaming from masked faces all around. Showing signs of illness among others produces quite a stigma these days, which is understandable in many ways. People are now staying home more often when sick. The handshake is rarely socially acceptable. We sit spaced as far apart as possible. Plexiglass dividers are everywhere. We wipe surfaces and wash our hands more. All of these actions help reduce the spread of Covid-19, but because influenza is primarily transmitted through contact and droplets rather than droplets and aerosolization, these efforts curb flu transmission even more.

Fewer cases in the Southern Hemisphere

Each year, flu cases south of the equator are a harbinger of what the Northern Hemisphere will experience approximately six months later. The flu vaccine in the United States is designed based on the prominent strains identified in southern nations during the preceding season. The low activity observed this season in the United States is no surprise when considering the dearth of cases in the Southern Hemisphere earlier in 2020. In Western Australia, flu declined by 99.4% compared to 2019. Furthermore, among 83,307 flu tests conducted across South Africa, Australia, and Chile during the 2020 season, an astounding 51, or 0.06%, returned positive. This is a tiny fraction of the 13.7% that typically return positive based on data from the preceding three years.

So, was Dr. Fauci wrong to be so concerned about the flu this year? Absolutely not! In fact, we have Fauci and many other health care experts to thank for what’s happening now. Recall the adage “an ounce of prevention is worth a pound of cure.” Our one-ounce investment in prevention by way of vaccines, masks, distancing, and hygiene has produced a big payoff. The near absence of a flu season is our pound of cure, and it couldn’t come at a better time.

Husband, Father, Health and science writer, Interpreter of medical jargon, Hospitalist physician, Board certified in internal medicine and pediatrics

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