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November 28, 2022

Testing for Covid-19 at home is easy. Why can't we test for the flu too?

Daily Briefing

    During the pandemic, many Americans grew accustomed to testing for the coronavirus at home. And since rapid antigen flu tests at physicians' offices are "virtually identical" to at-home Covid-19 tests, the same technology could likely be applied to at-home flu tests. Writing for STAT, Brittany Trang explains the challenges associated with developing and approving these at-home tests for different respiratory viruses.

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    As Covid-19, flu, and RSV cases continue to spread in the United States, "it would be helpful if Americans had a way to distinguish between different ailments at home," Trang writes.

    At-home flu testing could lead to better use of antiviral medications for influenza, ensuring that those who get it "are the ones who need it the most," said Christina Yen, an infectious diseases doctor at the University of Texas Southwestern Medical Center. She added that at-home tests could also ensure "that we are making our treatment decisions based on data."

    However, at-home flu tests are not currently available in the United States. According to Zoë McLaren, an associate professor of public policy at the University of Maryland Baltimore County, the rapid antigen flu tests at physicians' offices are "virtually identical" to at-home Covid-19 tests, which can be purchased over the counter. In theory, the same technology could be applied to at-home flu tests. 

    Ultimately, "the issue comes down to historical hangups — and the need to find digital fixes to address them," Trang writes.

    "It's really rare, and it's really new, that people are allowed to know about what's happening inside their body without a physician in the middle," said Michael Mina, a former assistant professor of epidemiology at Harvard University. In the past, FDA has been slow to approve over-the-counter tests, Mina noted.

    In 2016, an FDA advisory panel was divided on whether the benefits of over-the-counter flu tests outweighed the risks, Trang writes. "Meeting transcripts show that as experts debated whether at-home tests would actually be effective at keeping people at home if they knew they or their children had the flu, one panelist joked that daycare centers might make the decision for parents if over-the-counter tests were available," she adds.

    "The woman is going to want to go to work, and she wants to drop her kids off at daycare," the panelist said. "The daycare, when they sign their contract, [could say] 'If your kid has symptoms, we're going to test him,'" and send the child home if they received a positive test result.

    While the panel laughed at this scenario in 2016, it "is not so laughable in the wake of the pandemic," Trang writes. At the peak of the omicron wave, roughly 1 in 4 symptomatic individuals tested themselves for the coronavirus at home, according to CDC. "Many Americans have clearly gotten accustomed to the idea of at-home testing, and to the fact that they may have to adjust their plans if they get a positive result," Trang notes.

    Still, regulators and clinicians have concerns about at-home tests. For instance, the tests can be less accurate than those administered by a health care worker because some people may not collect a large enough sample to get a valid result.  In addition, clinicians are better equipped to interpret false results. "They might order a more sensitive test, act with more caution for people they know are high-risk, or decide to treat a patient anyway because they suspect a false negative," Trang writes.

    "There's also a historical concern about rapid influenza tests having low accuracy and varying in sensitivity from year to year," she adds. "Before 2009, measuring viruses by cell culture was the decades-old standard — but cell culture numbers could vary widely depending on how good the lab was at cultivating cells."

    In particular, year-to-year fluctuations in flu tests could become a concern if people use old tests, which may be less accurate.

    Will at-home tests become available in the US?

    According to Mina, there may be ways to improve the accuracy of at-home tests. For example, eMed, where Mina currently serves as CSO, is attempting to address at-home testing errors by connecting patients with a telehealth professional proctor to help interpret the results of every test they sell.

    "It's kind of like [the FDA] still lives in a world where the internet and telehealth doesn't exist," Mina said. "There are ways to get people testing at home that don't require the person to be in charge of interpreting the results all on their own."

    While it is still unclear whether FDA will approve at-home flu tests, a senior FDA official said that the agency is currently exploring options to help bridge the gap between the approval process for in-person and at-home tests. According to the senior official, FDA "strongly supports" at-home tests for respiratory viruses.

    "I'm glad to hear they said that," said Wade Stevenson, SVP of marketing at rapid-PCR test manufacturer Visby Medical.

    "When you put a new idea in front of the FDA, generally, they're excited about it," said Stevenson. "They like to see new ideas. And they do not want to play the role of, 'No, this is never going to work.' They want to encourage development and people pushing boundaries."

    Still, "manufacturers are frustrated about what they say is a lack of clarity surrounding the pathways to approval for over-the-counter tests and constantly shifting goalposts," Trang writes. (Trang, STAT, 11/22)

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