Are Variants Really Causing the Surges?

 

It's hard to find a story about surging COVID-19 that does not site variants as a cause.  Here's a sampling of headlines:

• Inslee warns of fourth Covid surge in Washington as variants spread (Washington State)
• COVID variant likely driving current case surge, Ballad officials say (Tennessee)
• Whitmer says Michigan’s COVID-19 surge is due to variants and non-compliance, ‘not a policy problem’ (Michigan)

If all of these claims are true, then we should be able to observe it: States that have have more variants should have bigger surges.

To test this, I got two pieces of data from the CDC for each state. First, from this page I got the "variants of concern" for each state where data was listed.  CDC only included states that, in their judgment, had a sufficient number of samples sequenced to make the numbers meaningful.

The data covered four weeks ending March 27.  "Variants of concern" (VOC) are ones for which there is sufficient evidence that the mutation causes the disease to be more contagious, and/or evasive of immune responses, and/or capable of causing more severe disease.  These include the UK, South Africa, California, and Brazil variants.

Second, for each of the same states, I calculated the one-week change in new cases per 100K, 7-day average, for the week ending March 27 using data from the CDCs Socrata API. To make for a reasonable visualization, I summed the values for the variants.  So that data point is the percent of sequences that show any of the VOCs.

Here is the resulting chart:

As you can see, the VOCs and surge size don't line up very well. In Arizona and California, we have some of the highest proportions of VOCs but the smallest surges. In New Jersey and Rhode Island, there are big surges, but their VOCs are below many of the other states.  

This graph is limited because the surge values and VOC values are plotted on the same scale but should be on separate scales. Even so, if there is a relationship, we should see the same pattern of variation in both variables across the states. 

Yet we do not. In fact, if I calculate a correlation between these two variables it is negative (r = -0.13), suggesting the more variants you have the lower your surge is.

I'm not arguing that variants have nothing to do with the surges. But it seems like an oversimplification to say they are the main factor or the only factor. Doing so implies it's all the disease's doing, and absolves us people of any responsibility. But as we know too well, mitigation behavior of people is a very important factor too.

Header Image by Roger Mosley from Pixabay