The Perfect Enemy | I’ve never tested positive for COVID. Is there a way to know if I’ve ever been infected?
September 29, 2022

I’ve never tested positive for COVID. Is there a way to know if I’ve ever been infected?

I’ve never tested positive for COVID. Is there a way to know if I’ve ever been infected?  San Francisco ChronicleView Full Coverage on Google News

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Dear Advice Team: To my knowledge, my husband and I haven’t had COVID yet. We’re fully vaccinated, have had exposures and have tested many many times. I’m wondering, if you haven’t tested positive, is there any way to know if you’ve had an asymptomatic case?

Welcome to Pandemic Problems, an advice column that aims to help Bay Area residents solve their pandemic and post-pandemic conundrums — personal, practical or professional. As COVID evolves into an endemic, we know readers are trying to navigate the “new normal.” Send your questions and issues to

Today, The Chronicle’s Annie Vainshtein fields a question about whether there’s a sure-fire way to tell if someone has been infected with COVID-19 in the past if they’ve never tested positive.

Dear Reader: What a great — and complicated — question! You’re not alone in your uncertainty. In April of this year, the U.S. Centers for Disease Control and Prevention estimated that 40% of the U.S. population had still not been infected with COVID-19, but that was before the highly contagious BA.5 variant, so that number could be far lower now.

Part of what makes infections so difficult to track on a national scale is the many different ways the virus can evade detection, especially if it’s an asymptomatic case. According to a study from the scientific research journal PNAS, the percentage of infections worldwide that were asymptomatic hovered at around 35%.

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So it makes sense that so many people like yourself may be wondering, 2 ½ years into the pandemic, whether they too, have had COVID-19 and just didn’t know it.

Experts I consulted said that there may be a way to see whether or not you’ve had COVID-19 in the past — but neither they nor the CDC recommend the method.

For starters, it may have only modest accuracy, according to Stanford infectious disease expert Julie Parsonnet.

How the test works is a bit complicated to explain, but here’s a brief overview from Parsonnet:

The coronavirus has numerous surface proteins that cause antibodies to be formed. One of them is the spike protein, which it shares with the COVID-19 vaccine.

By now you may have heard of antibody tests, most of which look in someone’s blood for antibodies to the spike protein. Before most of us were vaccinated, this test could be helpful in figuring out whether or not someone had had COVID-19 in the past. But people who have been vaccinated will develop antibodies to the spike protein, so it’s hard to differentiate whether or not you have antibodies because you’ve been vaccinated or because you were previously infected.

However, the virus has another protein on its surface, the nucleocapsid protein, that is not in the vaccine. If your blood contains antibodies to this protein, in addition to the spike protein, then you would have likely have had an infection, said Parsonnet.

Now, the caveats: It’s unclear whether or not these antibodies wane over time. If you had an infection a long time ago, the antibodies could be gone, said Parsonnet. She added that people with milder infection also tend to produce lower levels of antibodies, so it may be that you never produced enough to find the anti-N (nucleocapsid) antibody, even if you were infected recently.

And for what it’s worth, experts say they’re doubtful that any antibodies measured in a commercial lab setting would be good predictors of how immune or protected someone is from the virus. According to UC Berkeley infectious disease expert John Swartzberg, it’s only more sophisticated testing done for research that would be able to measure the extent of people’s protection from the virus, rather than relatively “simple” tests that are easily reproducible and can identify infection — but not the degree of protection.

“I would tell people to not waste your money,” said Swartzberg. “It’s not going to give you any information that’ll tell you how to live your life.”

Swartzberg said that before people seek out a nucleocapsid test, which could be costly and cause more confusion, he would advise them to think about what they’re trying to figure out, and why.

He said he would also advise people to ask themselves how the information they might receive would change their decision-making: would it change their choices about avoiding COVID? About getting boosted? He would also advise them to remember that these are “not absolute answers.”

Again, overall, experts did not recommend the use of these tests, and urged people to continue to follow their vaccination timelines. Plus, even if people find that they were infected in the past, they can still be reinfected within a matter of months — even from the same strain — according to Dong Heun Lee, an expert of infectious disease at UCSF.

“Humans are really curious animals, and getting answers to questions gives us some degree of comfort and control,” said Swartzberg. “Whether it’s fiction or not.”

Pandemic Problems is written by Chronicle Advice Team members Annie Vainshtein and Kellie Hwang, combining thorough reporting and guidance from Bay Area experts to help get answers and find a way forward.