COVID-19 Update: Fall Surges Across the World

From the very start of the pandemic, the most important unknown was the number of mild or asymptomatic cases that were being missed by testing. 

  • If the number of missed infections was high, then the disease was less deadly, and population immunity levels were higher.  
  • If the number of missed infections was low, then the disease was more deadly, and population immunity levels were lower.
We did our best to figure this out, and you can look back through my blog history to see how I wrestled with the question. 

During the summer, cases simply did not rise at the rate I would have expected, and I began to ask questions like whether it was possible that cross immunity to other coronaviruses had created a large fraction of the population that had pre-existing immunity. I simply could not understand why cases weren't rising faster than they were (given our behavior). Yes, we saw cases go up in NEW locations that had not yet hade major outbreaks. But places with large outbreaks were remarkably resistant to new infections, despite only having had a small fraction of their population that were infected. 

I still don't understand it. 

But whatever the reason, it is no longer the case. 

And this new data punctuates the utter failure of the Sweden model. 



It also means that I will likely need to adjust my approach for estimating true infections from cases (and testing rates) soon. After all, my old approach now estimates that over 90% of North Dakota has been infected, which seems impossible. 


What happened here? My model assumes that the higher the fraction of tests that are positive, the more infections are being missed by tests. While this is true, North Dakota completely broke my model when their % of tests positive literally went off my scale, exceeding 30%. They are now pushing near 70%!

With near 70% of tests positive, my model is assuming that the true number of infections is 13 times the number of confirmed cases. But at this rate, North Dakota's estimated percent infected would surpass 100% in the next month. 

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