Most of us have already had a case of COVID

From the Johns Hopkins daily health newsletter:

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US SEROPREVALENCE 

A study published April 26 in the US CDC’s Morbidity and Mortality Weekly Report (MMWR) estimates that 58% of the US population, including 75% of children, have been infected with SARS-CoV-2. Many of those infections occurred during the winter’s Omicron surge. The study reports on data from national commercial laboratories across all 50 states, Washington, DC, and Puerto Rico. Between September 2021 and February 2022, labs conducted convenience samples on blood specimens that were submitted for clinical testing in their labs, excluding samples that were testing for SARS-CoV-2 antibodies upon initial receipt. The median sample size for the group of labs was 73,869 each month, with a drop in the number of tests to 45,810 in February 2022, likely caused by disruptions from the surge in domestic infections fueled by the Omicron variant. The research team weighted samples by demographic data to produce estimates of seroprevalence. 

The team saw a slight, but steady, increase in seroprevalence between September and December 2021, increasing between 0.9-1.9% every 4 weeks. At the end of this collection period, the seroprevalence across the US sample was estimated to be 33.5%. Between December 2021 and February 2022, at the height of the Omicron surge, the team observed a spike in national seroprevalence, rising from 33.5% to 57.7%. Notably, during this period, children aged 0-11 saw an increase from 44.2% to 75.2% and those aged 12-17 saw a similar increase from 45.6% to 74.2%. Adult populations saw spikes in seroprevalence from 36.5% to 63.7% for individuals aged 18-49, 28.8% to 49.8% for those 50-64, and 19.1% to 33.2% among those aged 65 and older. The researchers noted several limitations in their study design, including restrictions of applicability tied to convenience sampling; limited race and ethnicity data; the potential for sampling bias due to the setting of sample collection; and the possibility that infection following vaccination resulted in reduced antibody titers.  

SARS-CoV-2 testing is only able to catch a fraction of cases occurring in the country, so serosurveys present an opportunity to better understand the scale of infections. Still, the study may not represent a full picture of COVID-19 in the country, nor does it indicate whether or not individuals with SARS-CoV-2 antibodies have persistent immunity to new infections. CDC Director Dr. Rochelle Walensky noted the study’s results and vaccine uptake show an increased level of community protection from SARS-CoV-2. She added that vaccination remains key in creating a more resilient population, urging those who remain unvaccinated, including those previously infected, to get vaccinated. 

COVID-19 Numbers in the US do not seem to be growing exponentially

Looking at the past month of CDC-reported infections and deaths from the new corona virus, I conclude that there has been some good news: the total number of infections and deaths are no longer following an exponential growth curve.

The numbers are indeed growing, by either a quadratic (that is, x^2) or a quartic (x^4) curve, which is not good, and there is no sign of numbers decreasing.

BUT it looks as though the physical-social distancing and self-quarantining that I see going on around me is actually having an effect.

Yippee!

Here is my evidence: the actual numbers of infected people are in blue, and the best-fit exponential-growth equation is in red. You can see that they do not match well at all. 

total cases US not looking exponential

If they did match, and if this were in fact exponential growth, we would have just about the entire US population infected by the end of just this month of April – over 300 million! That no longer seems likely. Take a look at the next graph instead, which uses the same data, but polynomial growth:

total cases US looking second power

Just by eyeballing this, you can see that the red dots and blue dots match really, really well. When I extend the graph until the end of April, I get a predicted number of ‘only’ 1.5 million infected. Not good, but a whole lot better than the entire US population!

Also, let’s look at total cumulative reported deaths so far. Here are the CDC-reported numbers plotted against a best-fit exponential curve:

deaths do not seem to be exponential

Up until just a few days ago, this graph was conforming pretty well to exponential growth. However, since about April 8, that seems to be no longer the case. If the total numbers of deaths were in fact growing at the same percentage rate each day, which is the definition of exponential growth, then by the end of April we would have 1.5 million DEAD. That’s THIS MONTH. Continued exponential growth would have 1.2 BILLION dead in this country alone by the end of May.

Fortunately, that is of course impossible.

Unfortunately all that means is that the virus would run out of people to infect and kill, and we would get logistic growth (which is the very last graph, at the bottom).

death seem to be 4th power polynomial

This fourth-degree mathematical model seems to me to work much better at describing the numbers of deaths so far, and has a fairly good chance of predicting what may be coming up in the near future. It’s still not a good situation, but it shows to me that the social and physical distancing we are doing is having a positive effect.

But let’s not get complacent: if this model correctly predicts the next month or two, then by the end of April, we would have about 60 thousand dead, and by the end of May we would have 180 thousand dead.

But both of those grim numbers are much, much lower than we would have if we were not doing this self-isolation, and if the numbers continued to grow exponentially.

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FYI, a logistic curve is shown below. Bacteria or fungi growing in a broth will grow exponentially at first, but after a while, they not only run out of fresh broth to eat, but they also start fouling their own environment with their own wastes. WE DO NOT WANT THIS SITUATION TO HAPPEN WITH US, NAMELY, THAT WE ALL GET INFECTED!!!

logistic curve again

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