As COVID-19 case numbers have slowly risen in the United States, Americans are turning to home antigen rapid tests to find out if they have an old-fashioned cold, flu, allergies — or COVID-19.
Though such at-home tests used to be hard to come by due to supply chain issues and the mismatch between supply and demand, the Biden administration’s investment in millions of free tests that Americans can request through the Postal Service has made them ubiquitous.
As such, many American families have adopted a now-familiar pandemic ritual: someone in a household develops symptoms, takes a home test, then tests negative and goes about their lives; or test positive and self-isolate.
However, this seemingly simple routine is not so if the tests do not work very well. Many Americans have reported — sometimes repeatedly — false negative results from their home tests. In April, ESPN reporter Alexa Phillipou reported “Test[ing] positive for COVID after two negative tests at home.” Writer and podcaster Lindzay Gibbs reported similarly tested positive at home after testing negative two days in a row.
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As the pandemic lags, the unreliability of home testing has turned what should be a simple task into a frustratingly nuanced statistics game. Experts therefore say that testing negative at home does not necessarily mean one is free of COVID-19. Often only after symptoms worsen and other possibilities have been ruled out does a second test—or third or fourth—give a positive result.
This repetitive testing ritual can be costly. Once someone has exhausted their free state tests — which, incidentally, you can order more regularly — it can cost a family of four almost $100 to take two tests each. Once someone tests positive, more people in the household are likely to develop symptoms.
With versions of this hypothetical scenario playing out in homes across America, it’s a normal question to ask: Is at-home testing even worth it at this point—financially, emotionally, and logistically?
Nathaniel Hafer, an assistant professor of molecular medicine at the University of Massachusetts Chan Medical School, and Apurv Soni, an assistant professor of clinical informatics at the same institution, who both studied antigen and polymerase chain reaction (PCR) testing, say yes to Salon — but note a few Limitations.
“One of the reasons for this is that our group here at UMass did a study over the winter in which we looked at the performance of three main types of tests compared to Delta and Omicron,” Hafer told Salon. “We felt that the study showed that the tests can detect omicron and that they perform similarly whether it’s the delta or the omicron period.”
In other words, the false negative results are not necessarily due to the subsequent mutations of SARS-CoV-2, but for reasons related to the sensitivity and mechanics of these tests. Hafer and Soni’s research adds to a growing body of research suggesting that if a person were infected with COVID-19, the infection would likely test positive on a PCR lab test 48 hours before an antigen test at home. Because PCR tests are able to detect the smallest amounts of virus material by amplifying the genetic material samples.
“We know that SARS-CoV-2, just like any infection, takes some time to build up in the body after someone gets infected, and that’s really the lag that people are seeing.”
While PCR tests are considered the gold standard for detecting the virus, they require more time and support to work and a laboratory environment. However, this means that PCR tests can detect even the smallest traces of the virus. Samples for PCR testing can be collected at home, but must be analyzed in a lab.
The main benefit of at-home antigen testing is the ability to provide a result within 15 minutes — although these tests can only detect the viral proteins present in the sample and don’t amplify them like a PCR test.
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Often, home testing cannot detect COVID-19 until a person’s symptoms begin and they are at their most contagious. Yet someone with COVID-19 could be contagious before they start showing symptoms. The researchers estimate Omicron’s incubation period, which is the period from which a person is exposed to the virus and then develops symptoms, to be around three days.
“The over-the-counter test doesn’t have an amplification step like PCR or the molecular tests out there,” which are “extremely sensitive because they amplify genetic material,” Hafer told Salon. Hafer explained that the home tests are “inherently less sensitive.” “We know that SARS-CoV-2, just like any infection, takes some time to build up in the body after someone gets infected, and that’s really the lag that people are seeing.”
Soni and his colleagues conducted a study that found that home testing prevented about 40 cases per day, compared to communities where home testing was not commonly used.
Previous estimates suggest that at-home antigen tests like BinaxNOW or QuickVue have an 85 percent accuracy, meaning they miss about 15 in 100 people infected.
Soni said the “bottom line” is that home testing is still “very useful” and “critical” in part because of accessibility. Since April, many COVID-19 testing sites (i.e. PCR tests) have been closed.
“Another point I would like to make regarding the usefulness of rapid antigen testing is more at the population level,” Soni said, explaining that he and his colleagues conducted a study that found that home testing reduced about 40 Cases prevented a day, compared to communities where at-home testing was not commonly used. “At the population level, we definitely see rapid antigen testing as critical,” Sonia added.
Still, Soni feared there wasn’t enough guidance for Americans on how to use them most effectively. First, just because you tested negative doesn’t mean you don’t have COVID-19; If you’ve been in contact with someone who tested positive but tested negative, Soni said you should have another rapid antigen test within 24 to 48 hours. Meanwhile, he said people should wear masks indoors and isolate themselves from others.
“Masking prevents transmissibility, and while transmissibility is possible if the antigen test is negative, the chances of it happening are much lower,” Soni said. “So between confirming it’s a negative antigen test and masking it, you reduce the risk of spreading the virus to other members in your household or to people you interact with.”
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