Covid Cases In US May Have Been Undercounted By 60%; Reported Cases 'Represent A Fraction of Total'
The Guardian, July 26, 2021. Number of reported cases ‘represents only a fraction of the estimated total number of infections.’ After rapid rollout, why has the US vaccine effort stalled?
The number of Covid-19 cases across the US may have been undercounted by as much as 60%, researchers at the University of Washington have found. The study, published in the Proceedings of the National Academy of Sciences, builds on research which has found the number of reported cases “represents only a fraction of the estimated total number of infections”. It has important implications for how many Americans need to be vaccinated to stop outbreaks.
The paper comes as a swath of states across the south and midwest, especially Arkansas, Missouri and Louisiana, experience outbreaks driven by Delta variant infections among unvaccinated people. “There are all sorts of different data sources we can draw on to understand the Covid-19 pandemic,” said Adrian Raftery, a professor of sociology and and statistics at the University of Washington and senior study author. But, he said, “each source of data has its own flaws that would give a biased picture of what’s really going on. What we wanted to do is to develop a framework that corrects the flaws in multiple data sources and draws on their strengths to give us an idea of Covid-19’s prevalence in a region, a state or the country as a whole.”
The study incorporated data on deaths, the number of tests administered each day and the proportion that come back positive. Importantly, it also incorporated data from studies of people randomly sampled for Covid-19 in Indiana and Ohio. Random sample surveys provide strong evidence of actual prevalence of a disease because they do not rely on people seeking out tests, which often fail to capture asymptomatic infections.
Based on analysis of that data, researchers found as many as 65 million Americans may have been infected. Official tallies put the number at about 33 million. The University of Washington researchers estimated that 60% of all cases were missed, with only one in every 2.3 cases counted in Indiana and Ohio...
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https://www.theguardian.com/us-news/2021/jul/26/us-covid-cases-undercounted-study
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Any time you set out to count, individually and cumulatively, any set of events, it is virtually certain you will undercount. That is the nature of observing and counting and not extrapolating. The harder it is to spot the events when they do happen, the greater the undercounting. And you have to actually do a test in order to even possibly record a positive result, so... you know. 
A lot of undercounting will happen from untested people.
A 60% undercount sure seems bad. But India, for example, is undercounting by approximately tenfold just on deaths, so when you grade on a curve we are "pretty bad" rather than "very bad" or "terribly bad" -- but it sure would have been nice to be "not bad at all."
