C19 and Pandemic Influenza Epidemic Curves

Note: CDC had changed the structure of a data file this week, which made the percentage of ED visits break in my state files. I looked at trying to fix them all, but then realized that there will likely need to be a massive data overhaul in about a week since hospitals are required to report data again. This will require a complete rebuild of the file for each state, so I decided to just wait and see what kind of data is available next week.

Epidemic curves are simply a means to represent cases or deaths over time. For example, are the deaths from the Spanish Flu from different cities. Note at the peak in NYC, the mortality rate was running about 6%.

It’s also worth pointing out there there was a small wave in late June/July which can be more easily seen here.

That’s almost reminiscent of how smaller waves preceded both the delta and omicron waves from COVID, which also disproves the claim that viruses get milder over time. It’s also worth pointing out that once rapid tests came out, that cases really don’t paint an accurate picture of the burden of COVID in the US anymore, which is why I plot wastewater, positivity, and ED visits on the site.

Another way to analyze the impact of a disease is to view deaths by age group. Normally, influenza has a U-shaped curve, with most of the deaths occurring in the very young and very elderly, as represented by the dotted line on the graph below. During the Spanish Flu pandemic, there was a w-shaped curve (solid line), with a disproportionate amount of death in the young and healthy. In this case, the likely cause was a cytokine storm driven by the virus. Those with developed, healthy immune systems were at higher risk of this outcome as the immune system over-responded to the infection. In fact, the damage was so sever that the lung tissue from those victims looks like it had been exposed to chemical weapons.

A Brief Aside about COVID Mortality

Here’s a graph of COVID acute mortality in the US. COVID deaths are undercounted for a number of reasons, contrary to minimizers claims. Yes, a few get miscategorized, but that is the exception rather than the rule.

The red line on the right is what I want to emphasize and is my expectations for the future. COVID causes MANY chronic diseases as well as immune system disruption. The line represents the climb in chronic disease deaths from these sequelae. Acute COVID deaths will likely continue their normal wave patterns (unless we get a much better vaccine) built on top of these deaths. This of it as the x-axis curving up due to chronic disease deaths. Of course, these will likely be undercounted as COVID deaths as well. This is a VERY different pattern than what we see with seasonal influenza. It can cause other problems, but that generally happens within a few months of infection, such as a rise in acute myocardial infarction deaths, which are related to the inflammatory process of influenza. COVID is different in that it causes small clots in blood vessels, leading to focal tissue damage, death, and scar tissue from oxygen starvation, which will take a number of years to manifest.

A H5N1 Curve

People will notice a very obvious difference with a H5N1 pandemic compared to COVID if it starts and maintains the mortality (25-50%) we have seen in the past. In addition, it is spread more readily than COVID because it is also spread by contact and fomites, which suggests it will be much more transmissible.

That would result in a much higher and narrower wave of death. To illustrate that in comparison to COVID, something like this would not be surprising. That will cripple healthcare instantly and will make the supply chain problems we had since the start of the pandemic look like child’s play.