Updated: Jun 12, 2020
Welcome to Part 2 of our COVID-19 Transition series! Today we’re inspecting the Venn Diagram, if you will, of SARS-CoV-2 (the virus that causes COVID-19) and seasonal Influenza.
The title is a fair point in some ways. Flu is bad. The CDC estimates that there were somewhere between 39,000,000-56,000,000 cases of flu and 24,000-62,000 deaths related to flu in the most recent flu season, October 2019-April 2020. Many of these deaths are among vulnerable populations, including older adults and those with chronic illnesses. Sounds familiar. And yet, we really don’t enforce nationwide lockdowns for seasonal flu and other bacteria and viruses with which people are more familiar. So, is the entirety of the scientific community out for blood to ruin everyone’s beach vacations against the best evidence, or is there something else going on here (hint: something else going on).
There are definitely similarities. They’re both viruses. They both have the most concerning effects on people through the respiratory system. They are both primarily spread through contact with the infectious particles and by droplets, like through sneezing and coughing.
However, there are critical differences. One of the main differences is in reproductive rate. This refers to how many people, on average, the virus will be passed to from an infected person. For seasonal flu it’s around 1-2. For COVID-19, we’re not too sure, but experts believe it’s around 2-4 (probably closer to 2). This may not sound like a lot, but think about how having a third more distribution in moving from person to person affects community spread over multiple generations of infection. And now, add the fact that there is really no baseline human immunity to this new strain of coronavirus, whereas there is baseline immunity to influenza in the community through exposure, as well as through vaccines. This protection creates a sort of roadblock where transmission is interrupted and prevents many opportunities for potential infections. Vox has actually done a great job with this video to help give a visual of these concepts:
Part of the problem also lies in the uncertainty and wide ranges of data we’re seeing with COVID-19. Flu can incubate for a couple days, usually, before causing symptoms. When we feel crummy, we stay home (hopefully), and we limit spread. SARS-CoV-2 will typically cause symptoms within 5 days, but can incubate for up to 14 days in the body before causing symptoms. During this time, individuals who appear healthy, with the best intentions, are potentially and unknowingly infecting those with whom they come into contact.
And when it comes to how sick people are getting, the story becomes even clearer. With the flu, about 2% of those affected will become sick enough to require hospitalization. And luckily we have a medication, Oseltamivir, that can work pretty well at limiting duration of symptoms and potentially spread. Severe flu illness can be devastating and leads to a mortality rate of 0.1%. With COVID-19, we have yet to find a medication that is reliably effective at reducing mortality. Some strides are being made, but we are far from definitive medication options that reduce mortality or provide preventive benefit. COVID-19 leads to hospitalization in about 20% of infections, with 5% considered critical, and has a mortality rate over 10 times higher than flu at around 1-2%. As you follow this series, think about your friends and family. You probably know a hundred people.
In April, almost one out of three deaths in the United States every day involved COVID-19 - and with lack of test availability, this may be an underestimate.
So COVID-19 is far deadlier than seasonal flu and has different fundamentals to its transmission. This leads to a completely different set of behavior recommendations from a public health perspective. We don’t have a vaccine or preventive medication yet, like with the flu, meaning we can’t break transmission episodes, so our goals have become to prevent that transmission episode from occurring or prolong the time periods between these occurrences. Long story short, if a viable medication and/or vaccine were introduced, social interventions would be more similar to how influenza is addressed, but for now social distancing, adequate testing and contact tracing are the mainstays of addressing the pandemic. When there’s no immunity in the community, you need social distance for continued existence – or something like that. And with that, I hope you’ve all had a delightful Mother’s Day. We'll catch you in part 3.