The 3rd COVID-19 peak — is it really different from the first two?

The numbers across the U.S. today show an increase in COVID-19 infections that appears to be a “3rd peak” occurring since the pandemic started in early March. The dynamics of this 3rd peak, which has been called the 2nd wave by some media outlets, are interesting and deserve further discussion.

The beginnings of the 3rd peak of COVID-19 infections in the USA Also note the numbers of deaths and tests per day.

When one looks at the number of infections over time, it appears that the second peak in COVID-19 infections that happened over the summer (mainly in Southern states) was the largest in the U.S. It also seems that this third peak of infections may rival the second in size. However, the number of infections documented in the U.S. in the summer was possibly an increase over the first peak only because the amount of testing was much greater. 

Could these second and third peaks actually be smaller than the first?

We are currently doing 10 times as many COVID-19 tests per day as we were during the first peak of the infection in March and April. Given that the rates of positive tests are slightly less than they were in most stricken areas in April, we could be detecting two to three times as many COVID-19 cases as we did in April. The result would be the appearance of more cases.

Also suggesting that the three peaks might not be different in size is the number of deaths currently being reported. COVID-19 deaths were much lower per infection during July than April, and while this may be due to better care of patients (and younger patients), it may also be because the overall number of infections was actually less and only the number of detected infections was higher.

In addition, while the number of infections has risen significantly over the past two weeks, the death rate has not begun to climb. This may be due to a delay in deaths vs. infections, but could also be because the case fatality rate is actually lower than we thought, and we had many more undetected infections than we realized in March and April.

If all three of these peaks are essentially similar, one wonders if there is some limiting factor that may cause this third peak to decline like the first two? It could be that local immunity rises to a point where the virus is not efficiently transmitted. Or, maybe people seeing the infection numbers and hospitalizations rise actually get religion about social distancing and masks.

COVID-19 is not flu, and we should not try to predict the dynamics of this infection based on learnings from flu.

Published by jbakerjrblog

Immunologist, former Army MD, former head of allergy and clinical immunology at University of Michigan, vaccine developer and opinionated guy.

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