COVID-19: What's the Big Deal?

The proteins on the surface look like a crown, as in coronation

As is true for influenza, illness caused by COVID-19 can range from very mild to severe.  So why are we more worried about it than we are about seasonal flu?

The answer lies in part of the original name - before COVID-19 was adopted.  It was called "novel" coronavirus. Novel doesn't mean the virus likes to read fiction, any more than the "corona" part of the name means it's connected to Corona beer.

Novel means new. Not new in the big scheme of things. New to humans, after making the leap from an animal species.

How can that cause so much trouble?

It means that it is new to our immune systems.

Let's say we take a group of 100 people who are well, put them in a room, and then add a person with seasonal influenza. That person can spread the flu virus to the others in the room. But not so easily. Each time a person who comes into contact - of the sort that lends itself to transmission - with the infected "index case," either of two things can happen. The new contact gets infected, and experiences illness.

Alternatively, if the new contact has some immunity, through vaccination against, or previous infection with, the same or closely related flu strains, the new contact will most likely not get sick, and will not be a source of contagion that - like the index case - threatens everyone else in the room.

The presence of immunity among people in the room means person-to-person spread will be limited. Thus, what epidemiologists call the "attack rate" will be reduced. (This is what epidemiologists sometimes call "herd immunity.")

Now, take the same group of 100 well people and add a person sick (even very mildly) with COVID-19. Nobody else in the room has any immunity, because this is a "novel" virus. So person-to-person transmission happens much more readily, and thus the "attack rate" will be much higher.

So we can see that even if COVID-19 is no worse than seasonal flu in the average person, the "novel" attribute enables it to spread quickly to a large number of people. And that really matters, because a certain percentage of people who get infected will die. That is called the "case fatality" rate. No matter what the case fatality rate is, the more people who get infected, the more will die.

Right now we aren't really sure how the case fatality rate compares with seasonal influenza. We just don't have enough population data yet, and that makes it a moving target.

But there is reason to be concerned that it will be significantly higher than for seasonal flu. Again, this is because of the "novel" attribute.

It is believed that one of the reasons the Spanish Flu of a century ago, a novel strain, killed so many people - and especially so many young and previously healthy people - has to do with the immune response. If you have been exposed to other viruses that are similar, you will have a little bit of immunity. This helps in two ways. First, your immune system is at least a little "primed" to respond. Second, some of the immune system's response will be to produce partially-matching antibodies that can act as "blocking" antibodies that lessen the intensity of the overall immune response. And this is actually a good thing.

Why? Because a good bit of the effect of the virus on your body - especially on the respiratory tract - is the result not so much of the virus itself but the inflammatory aspects of the immune response. The "blocking antibody" effect can lessen the severity of the inflammation. You don't get that when you're infected by a novel virus. Since young, healthy people typically have the most intense immune response to any infectious agent, the lack of a "blocking antibody" effect means they can get very sick very quickly. Paradoxically, then, their risk of becoming seriously ill or dying may not be that much lower than it is for the elderly and infirm.

What does all this mean? If we start to see evidence of rapid "community spread" - and there is reason to think we will - the attack rate will be high, the number of cases will be high, and the number of deaths will be high.

So pay attention to all the advice you're getting from reliable sources on how to limit contagion.

For my entire career I have been telling patients and families who ask me how to avoid spreading an infectious disease from the "index case" in the family: "Lots of hand washing." This applies to everything from "pinkeye" to the common cold to influenza. And now to COVID-19.

Wash your hands!