How many have it?

In the early days of the pandemic, and even now in mid-April 2020, we heard many estimates of the risk of the coronavirus SARS-CoV-2. Some think maybe it’s like the flu. Others assert, this coronavirus is no flu.

When we say coronavirus is or is not like influenza, what comparison are we making? One comparison could involve the incidence of death from each disease. The question could be, how do the numbers of people who perish this week from each disease, COVID-19 vs. the flu, compare? What about over a whole year? If it turned out a lot more people died from COVID-19 than flu, you might conclude COVID-19 is no flu.

Another comparison could be about the rates of mortality instead of total numbers of infection. This question would be, what is the chance of dying if infected by COVID-19 vs. flu? In order to answer that, you need to know how many people have been infected with coronavirus and we haven’t known that.

Until now.

Dr. John Ioannidis and his co-authors published on April 17, 2020 a serology study of the population of Santa Clara that identified, using antibody tests, how many people from their population sample had been infected.

COVID-19 Antibody Seroprevalence in Santa Clara County, California

This is just what we needed to know in order to quantify how lethal SARS-CoV-2 is, a statistic known as the Case Fatality Rate (CFR). Estimates of CFR based on so-called confirmed cases tended to over-estimate the Case Fatality Rate because the measure of confirmed cases excludes those who contracted the disease and got over it without going to the hospital. An inflated CFR over-estimates the risk, which can affect policy.

Here is Dr. Ioannidis’s announcement about the study.

The data show that infections in that region were 50-85 times higher than the number of confirmed cases reported for that time. That’s good news! When you divide the number of deaths in that population by this updated count, you come up with a Case Fatality Rate more like that of seasonal flu. Naturally, this news doesn’t serve any of the poor souls who tragically lost their lives to either of those diseases. What it helps us to do, though, is to determine policy based on real data instead of shot in the dark guesses.

Although the risk of death from contraction of coronavirus is on par with the flu, life with coronavirus sure doesn’t feel like life with just the flu. This has a lot to do with timing. COVID-19 appears so severe because the events are happening so fast. Hence, the motivation for social distancing, to slow that down.

Meanwhile in other news, chronic disease kills tons more of us than COVID-19 ever will. We never panicked about all the deaths from obesity, heart disease, diabetes, and cancer because they’re spread out over time. We don’t tend to be terribly concerned about chronic disease, at least not enough to do something to prevent it, until it hits us.

Maybe we should pay attention. With risk of death from COVID-19 elevated in conjunction with comorbidies like obesity, diabetes, and heart disease, there has never been a better time than now to become healthier.