Research ExplainedEasy to understand, visual summaries of the latest research studies.
The original paper was updated. The authors revised their paper based on community feedback. See the latest explanation.

This is a summary of "COVID-19 Antibody Seroprevalence in Santa Clara County, California"


What percent of Santa Clara County, California has been infected by SARS-CoV-2, the virus that causes COVID-19?

The study claims over 4%, but we still don't know. In the first US-based study trying to answer this question, serious concerns about the methods make real conclusions difficult.

Key takeaways

Why is this question important?

The question is important for two reasons:

  1. We don’t really know how many people have been exposed to the coronavirus. Due to a shortage of tests, many people with symptoms or suspected cases of coronavirus have not been tested, so the number of positive coronavirus tests probably underestimates the number of people who have had the virus. This can help decision makers understand how many people have the virus, which helps them make decisions about controlling its spread.
  2. How dangerous is coronavirus? This reason is related to the first. Since we don’t know how many people are infected, we can’t accurately calculate how common it is to suffer serious symptoms or die from the virus. This is really important for us to understand so that we can understand the risks of the virus and also try and prepare our hospitals for the number of people who might need medical help.

Getting more information about these areas would be helpful for public health experts, epidemiologists, hospitals, and political leaders to implement the correct actions to control the pandemic.

Our take

This study has come under heavy criticism from other researchers based on the techniques used to arrive at their conclusions, so let’s take a look at the strengths and weaknesses of the research.


This was an ambitious study that was among the first of its kind in the United States. It provides a template for future researchers to improve upon. The researchers attempted to control for some of the limitations in their testing and acknowledged some of the limits on the conclusions that can be drawn from their study.


There are several areas pointed out by other researchers that limit how sure we can be about the results in this study. We discuss these below.

What did the study do?

How was it reported?

The original paper is a preprint study. It has not been certified by peer review from other researchers, and information presented may be erroneous. Do not use it to guide clinical practice! Learn more →

Original Paper DOI10.1101/2020.04.14.20062463

COVID-19 Antibody Seroprevalence in Santa Clara County, California [PDF]

Additional Reading

For more details and technical discussion of the study, we recommend reading the following resources:


The study authors revised their paper after posting it. We have explanations for the following revisions:

Updates and Corrections

If you see a mistake or want to suggest changes, please contact us.

Share This Explanation

Copy Link Twitter Facebook LinkedIn


Like this explanation? Get notified when we post new ones!

Please enter a valid email address.

👍 You're all set!