At-Home COVID-19 Tests May Not Detect Omicron in Time

As the government rolls out 500 million rapid at-home antigen tests, results of a small study suggest that those tests will produce false-negatives that will enhance Omicron’s spread.

Omicron moves so fast that it may even outrun correct results from at-home rapid antigen tests, according to recently released data. A preprint study, which has yet to be peer reviewed, shows that someone can be infected with Omicron and spreading the disease for days before rapid at-home antigen tests detect the variant in the individual. The authors note that health systems need to adjust as quickly as COVID-19 adjusts with each new variant.

“The performance of COVID-19 diagnostic tests must continue to be reassessed with new variants of concern,” states the study, which was published on the medRxiv website.

Ironically, the findings were unveiled on the same day—Wednesday—that the Biden administration touted progress on its plan to distribute 500 million rapid at-home tests. “Deliveries of tests from manufacturers to the U.S. government will begin over the next week or so,” said Jeffrey Zients, the White House Coronavirus Coordinator, at a White House briefing. “Americans will start receiving free tests in the coming weeks.”

Zients promised that officials will do all they can to make distributing the tests hassle-free.

“Obviously, this is an unprecedented action: to have a half billion tests bought by the U.S. government and distributed for free,” Zients said. “And we’ll continue to do more and more to increase access to testing, given the extreme demand that’s been driven by the transmissibility of Omicron.”

Testing has been viewed as one of the cornerstones for beating back the pandemic, especially as it became clear that the vaccines wane over time. But will Omicron’s speed make the tests useless?

The study states that its objective “was to describe the discordance in saliva SARS-CoV-2 PCR and nasal rapid antigen test results during the early infectious period. We identified a high-risk occupational case cohort of 30 individuals with daily testing during an Omicron outbreak in December 2021. Based on viral load and transmissions confirmed through epidemiological investigation, most Omicron cases were infectious for several days before being detectable by rapid antigen tests.”

The study results might also be drawn into the debate about whether schools should reopen for in-person education. The CDC recently unveiled a test-to-stay program designed to keep children in school. The studies the agency used in launching that program deployed antigen tests.

In the study unveiled Wednesday, the 30 individuals worked in offices in San Francisco and New York (some worked at Broadway theaters). Participants received both the antigen test and the polymerase chain reaction, or PCR, for which people in some locales line up for hours to receive because it’s believed to be more reliable. PCR’s performance in the study bolstered that contention.

People who tested positive for COVID-19 via PCR were given an at-home test the same day and the day after, and all the at-home tests produced false-negative results. In 28 of the 30 cases, the levels of the virus were high enough that the infected individuals could contaminate someone else, which in fact happened in 4 cases—that study investigators know about.

Blythe Adamson, PhD, MPH, the principal epidemiologist at Infectious Economics in New York and an employee of Flatiron Health, an affiliate of Roche, tells STAT that “it’s absolutely likely there were many more than four transmissions. We named four because there were four that were confirmed through contact tracing and epidemiology investigation. There were likely many more.”

The first documented case of the COVID-19 variant in the United States occurred on November 29, 2021—8 weeks ago. In that short time, it has become the dominant strain in the US, elbowing Delta out of the way and accounting for 95.4% of new cases, according to the Centers for Disease Control and Prevention (CDC).

Anthony Fauci, MD, the director of the National Institute of Allergy and Infectious Diseases and the chief medical advisor to President Joe Biden, warned at the White House briefing that data showing that Omicron produces milder symptoms—“sniffles” is the word often used—can cause Americans to underestimate just how much damage the variant can do.

While noting the preliminary data from numerous sources saying that Omicron infection is less severe than Delta and other earlier iterations, Fauci said that the “big caveat is” the those milder symptoms “might be overridden by the sheer volume of the number of cases that may be of reduced severity but could still stress our hospital system, because a certain proportion of a large volume of cases, no matter what, are going to be severe.” (A point recently made by Kevin Kavanagh, MD, a member of Infection Control Today®’s Editorial Advisory Board.)

Many medical experts and the public had hoped that Omicron’s mild symptoms might be a way of getting the world to herd immunity.

At the same press conference, CDC Director Rochelle Walensky, MD, said that “we’re asking everyone to follow these four steps: Get vaccinated and get boosted if you are eligible, wear a mask, stay home when you’re sick, and take a test if you have symptoms or are looking for greater, extra reassurance before you gather with others.”

“Take a test”—but which one?

Adamson tells STAT that “with every new variant that comes, scientists have to question whether the things that were previously true are still true. This one has a different way it travels, a different mechanism of action of symptoms, it has different windows of transmission.”