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Wondering if You Could Have Had COVID-19 Last Fall?

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Neha Pathak, MD - Blogs
By Neha Pathak, MDBoard-certified internistApril 15, 2020
From the WebMD Archives

This post was updated on 4/27/20 to reflect new information.

As public health experts try to stop the spread of the virus that causes COVID-19, doctors are also working to curb the spread of misinformation.

One story that has recently spread rapidly suggests that many Americans may already have been exposed to COVID-19 in November and December of 2019. Many people are sharing stories on social media of unexplained fevers, or flu-like illness during those months and wondering if they may have had COVID-19 without realizing it.

A version of this story has spread in California, where some are suggesting that there may be a large segment of Californians who have already been infected, providing some level of “herd immunity.” The idea being that if there is already herd immunity we may be able to return to the previous routines of life sooner than current predictions (scientists suggest that 50-70% of people would need to be immune to COVID-19 to protect the population. Most experts estimate that only around 5% of the population has been infected at this point).

Though it’s tempting to believe these stories and hope for a quick end to lockdowns and “stay at home” orders, this type of misinformation can be dangerous. It can undermine the policies that have helped to make California a success story, such as instituting social distancing directives earlier than other places in the U.S.

When a reporter from Slate asked Stanford researchers to weigh in on this story, they explained that their research does not suggest that COVID-19 was in this country in the late fall or winter of 2019.

The science of genetics also provides information about the global spread of COVID-19 and allows scientists to track its path across the world. Based on minor mutations that subtly change the genetic code of the virus, researchers have traced the origin to China during the November and December time frame. All of their work is documented in a data source called Nextstrain, an open-source project that tracks the genetic evolution of infectious diseases across the world.

However, there is now new evidence that the virus may have been circulating in the U.S. as early as January and February. There may have been deaths related to the virus that have not been documented because we were not testing for COVID-19 during this time. There is also some evidence that many more people have been infected than previously thought. What all of this may mean is still not clear. We still don’t know if having had the virus once means you are immune to it in the future or what the long-term risks are even for those who had mild or moderate symptoms.

The biggest takeaway from these findings is that researchers are following every crumb to identify the origins and path of the spread of COVID-19 and trying to share this information as quickly as possible to keep people safe. 

Currently, researchers are working furiously to identify people who were previously exposed and possibly immune throughout the country. These findings will inform policies that can help us ease up and open the economy in a safe and effective manner. It is unlikely that we will safely achieve herd immunity without an effective vaccine.

You can follow Dr. Neha Pathak on Twitter @NehaPathakMD for regular updates about COVID-19 and information about other public health emergencies.



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About the Author
Neha Pathak, MD

Neha Pathak, MD, is a board-certified internal medicine doctor and part of WebMD's team of medical editors responsible for ensuring the accuracy of health information on the site. Before joining WebMD, Pathak worked as a primary care physician at the Department of Veterans Affairs and was an assistant professor of medicine at Emory University in Atlanta.

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