Antibody tests show coronavirus infections could be much higher than anticipated, reducing the death rate

Two studies regarding antibody testing in California have been released in the past several days. One from Stanford University and the other from the University of South California (USC). Both studies indicate that the number of people actually infected is much higher, which would reduce the mortality rate.

The USC Study tested people over a two day period at six sites.

Based on the results of the first round of testing, the research team estimates that approximately 4.1% of the county’s adult population has an antibody to the virus. Adjusting this estimate for the statistical margin of error implies about 2.8% to 5.6% of the county’s adult population has an antibody to the virus — which translates to approximately 221,000 to 442,000 adults in the county who have been infected. That estimate is 28 to 55 times higher than the 7,994 confirmed cases of COVID-19 reported to the county at the time of the study in early April. The number of COVID-related deaths in the county has now surpassed 600.

The Stanford Study tested 3300 residents in Santa Clara County.

The preliminary study, conducted by researchers at Stanford University, estimates that between 2.5% and 4.2% of Santa Clara County residents had antibodies to the new coronavirus in their blood by early April. Antibodies are an indication that a person’s immune system has responded to a past infection.

Though the county had reported roughly 1,000 cases in early April, the Stanford researchers estimate the actual number was between 48,000 and 81,000, or 50 to 85 times greater.

Using the numbers from the CNN Coronavirus Tracker, we created a spreadsheet that shows the current case totals and deaths to come up with the mortality rate. We then used the lower numbers on the range given by both studies to come up with an adjusted death rate that factors in the additional number of people infected.

DateTotal cases USTotal deaths USMortality rateStanford Study 50XUSC Study 28X10X
April 20, 2020786,968423085.38%0.11%0.19%0.54%
Deaths per 100,000 cases5376108192538
Total cases excluding New York533,777236554.43%0.09%0.16%0.44%

We used a factor of 50X the number of total cases for the Stanford Study and 28X for the USC Study. We also added a third column for 10X. The state of New York has a current death rate that is more than twice as high as the next closest state. We created a separate group that excluded the New York numbers.

By including in the potential for a higher infection rate, the death rate from Covid 19 drops substantially when compared to only those who have been tested. The mortality rate dropped from 5.38% to under 0.2% in both scenarios. More tests are being conducted in other parts of the country and USC will be testing residents every few weeks.

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