infectious Diseases
Did the flu disappear?

Did the flu disappear?

No. And when people use this as a rhetorical question to express their doubt about the severity or incidence rate of Covid-19, they actually showcase their lack of virology knowledge.

An appropriate question for those genuinely seeking a learning opportunity would be: “have influenza rates declined during the Covid pandemic, and if so, why?”

Great question! Yes. It appears they have. Anecdotally, as an ER nurse, I have cared for a countless number of covid patients and only 2, count em, T-w-o, influenza cases since October (the beginning of “flu season”).

On a broader scale, some influenza seasons get a “late start”, so it’s still possible/probable that we’ll see an increase in influenza cases as the winter moves on, weather gets colder and vaccines for Covid-19 are given out, causing people to abandon some of the protective measures associated with the current pandemic. But let’s move onto the “why” of things. Overall, we have seen less flu this season than most years – and there are perfectly reasonable explanations for that! (And no, it’s not because we aren’t testing, we are.)

Influenza is less contagious than Covid-19. There’s really no great elaboration that needs to be done here. There will, hands down, be more cases of a disease that is more contagious than another – every – single- time.

Half the country is vaccinated for influenza. Enough said there.

Influenza is spread by droplet. So is Covid-19, but in addition to droplet transmission, Covid-19 also spreads by airborne transmission. What does that mean? Droplets are large water molecules that carry a pathogen from point a to point b. Once those infected droplets leave our noses or mouths, they must travel to another person’s nose or mouth to make them ill. Masks cover the nose and mouth if worn properly and provide a barrier to large droplets entering our respiratory mucosa. Hand washing or sanitizing kills any droplets you may have on your hands, and standing more than 6 feet away prevents most heavy droplets from reaching you if someone sneezes or coughs in your direction. So these 3 measures nearly eliminate the transmission of influenza, and much of the transmission of covid-19. But remember, Covid-19 has another way of spreading that influenza does not enjoy; it’s airborne too.

Airborne viruses accumulate in the air around an infected person when they exhale. Forceful exhalation, which happens during yelling, singing, coughing, or talking very loudly, expels larger volumes of those tiny airborne viruses. Those airborne viruses can linger in the air around a person for impressive lengths of time.

The longer someone stays in that particular spot, especially if they are singing, laughing, yelling, or talking loudly, the higher the concentration of virus around them becomes. An exchange of a certain concentration of virus is needed to cause infection in another person. Regular masks are not designed to filter particles small enough for airborne transmission, and are not suitable to offer adequate protection against airborne viruses. For airborne viruses, healthcare workers use n95 masks that have a filtration rating that protects us against these tiny airborne viruses. So you see, you can sit 6 feet away from someone at a bar or church, you can wash your hands, and avoid touching your face and protect yourself quite easily from influenza, however none of those things are adequate to protect you from an airborne virus like Covid-19, since the virus spends time accumulating in the air of your space and just by breathing (even with a simple mask on) you can inhale these viruses and become ill.

Now you can see also from this example that the setting makes a really big difference. How many places can you think of where people generally sit or stand in one spot for a long period of time while also singing, talking loudly, laughing or shouting? Restaurants, bars, churches, sporting events, concerts….. these are all examples of environments where these things occur simultaneously. In addition, places where air sits stagnant (lack of ventilation) allow even larger accumulations of virus. Outdoors, normal air movement allows the airborne virus to become diluted or carried away, indoor spaces do not. The higher the concentration of virus, the more likely you are to become ill from inhaling it.

Epidemiologists are not picking on you. Nobody is singling out your favorite activities and depriving you of them as some sort of a sick punishment or revocation of your “rights”. Epidemiologists work with virologists and public health officials to give recommendations that help keep the public healthy based on what they know about the transmission of the pathogen in question. This is the reason that certain activities have been advised against, such as attending restaurants, bars, churches or other lengthy indoor events.

Now in contrast, when you grocery shop, you move often, rarely spending more than a few moments in one spot. If you’re practicing masking and hand washing during this activity you have stopped the droplet transmission, and if you make your trips quick and spend limited time in another’s air space by moving around, you are mitigating the risks of airborne transmission as well. Grocery shopping does not carry the same risk of airborne transmission as church, and it especially does not carry the same risk of transmission as eating/drinking establishments where you must remove your mask to participate in the activity at hand.

Now let’s talk about kids. 0-9 year olds are the super spreaders of the influenza world. A majority of influenza infections are spread to adults by children. Children are notorious for their poor hand hygiene, and lack of personal space boundaries. In the past, we’ve just accepted that. Enter Covid; we demanded behavior changes from children too. Masks are worn in most classrooms across the country. Regular access to hand sanitizer is now the norm, with cute songs and reminders about how and when to wash up. We’ve also moved desks apart and limited the number of children who eat together at a table. All of these measures have prevented our little influenza vectors from ever sharing their germs with each other. When we prevent influenza in children, it doesn’t come home to their parents and grandparents. This has also helped contain the droplet transmission of covid by children.

So what about airborne Covid transmission and children? Schools have invested heavily in ventilation/filtration which helps keep air in classrooms circulating, thus interrupting some airborne transmission. Certain activities like large assemblies and shouting or yelling or singing have been limited while in the classroom and these things are all helpful.

Influenza has not disappeared in the face of covid, however many of our Covid mitigation strategies have been MORE effective at reducing the spread of influenza than they have been at reducing the spread of covid. And that is why influenza appears to have “disappeared” when compared to Covid-19.

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