As omicron cases continue to sweep the United States, the Food and Drug Administration is urged to gather more information about the ability of home Covid-19 tests to detect the variant.
Evidence suggests that the omicron variant of the virus may appear in the throat before appearing in the nose. For this reason, the FDA has been lobbied to recommend swabbing the throat with the nasal swabs. But medical experts say anecdotes of people testing negative with a nasal swab at home but then testing positive with a throat swab can be misleading. FDA officials say there isn’t enough data to support the practice.
“We know that testing is resuming on omicron, but with less sensitivity,” Acting FDA Commissioner Dr. Janet Woodcock said Tuesday at a Senate Health Committee hearing. “What we need to do is see if the throat swab might provide more sensitivity.”
The FDA is investigating how at-home testing works like a throat test. If the results back it up, clearance could come quickly, Woodcock said. However, redesigning home testing to accommodate larger swabs would take longer.
None of the rapid home antigen tests available over-the-counter in the United States are designed for throat swabs. There’s also a reason medical professionals are the ones doing throat swabs for other infections, such as strep throat. Dabbing the back of your own throat is not easy to do.
“People shouldn’t use swabs designed as nasal swabs and try to swab their throats,” Woodcock said during the Senate hearing. “They can stab each other.”
The UK’s National Health Service recommends swabbing both the nose and throat when using a rapid antigen, or later, Covid test, the type used at home. But the agency doesn’t just recommend taking a sample from the throat. Earlier this week, Israel’s Health Ministry also advised people to swab their noses and throats when using rapid home tests.
“The virus grows in your nose and throat and somewhat on different time scales,” said Michael Mina, chief scientific officer of biotechnology software company eMed, who was assistant professor of epidemiology at Harvard TH Chan School. of Public Health. briefing on testing technologies this week. “My recommendation would be all FDA guidelines on this, but we also need to follow the science.”
Meanwhile, the FDA currently advises against taking throat samples when using a rapid home test.
“The agency recommends that individuals follow testing instructions closely,” FDA spokesman Jim McKinney told NBC News in an email. “We have always known that antigen tests have lower sensitivity than molecular tests. If people think they have Covid-19, they should take a follow-up PCR test to confirm their negative results. If a person tests positive with an antigen test, they should self-isolate and seek follow-up care with a health care provider to determine next steps.
It can be difficult to get a good throat sample if you are not a medical professional.
Dr. Jonathan Li, Brigham and Women’s Hospital
Dr. Jonathan Li, an infectious disease physician at Brigham and Women’s Hospital in Boston, cautions against changing the testing strategy that has been validated and cleared by the FDA. But he also noted that while he hasn’t seen data to support taking a rapid test sample from the throat, “theoretically it’s something that could be helpful.”
“What we have learned is that each variant seems to have its own characteristics, and it is important that we are not locked into the idea that we know everything based on what we have learned from the last variant. “, did he declare. “We don’t always want to fight the last war. If there is anything unusual about omicron, it is important to pursue it and determine if there is anything we should do differently with this variant.
Before advocating the modified approach, Li said, he would need to see data showing it was effective. User error will likely be higher with self-administered throat swabs compared to nasal swabs, he said.
“There’s no intrinsic reason that if you swab the back of your throat and that’s where a lot of the virus is, and you had a really good sample, that a throat swab wouldn’t work. not with a rapid test,” he said. “But usually people gag and it can be difficult to get a good throat sample if you’re not a medical professional.”
Another possible risk from home throat swabbing — residue from eating and drinking could cause a false positive, said Melissa Miller, chair of the American Society for Microbiology’s Clinical Microbiology and Public Health Committee.
“The nose and the throat have different pH levels and we’ve seen people take Coke or coffee and put it in an antigen test and a line comes up,” she said. “We don’t know exactly why this is happening, but the hypothesis is acidity.”
“I’m not saying it won’t turn out that you can use throat swabs, we just don’t know yet what impact that has on test results,” she said.
When should you do a Covid test at home?
Miller notes that a small preprint paper from South Africa, which has yet to be peer-reviewed, suggested that more detectable virus may reside in the throat than in the nose when a person is infected with the virus. ‘omicron compared to the delta variant, although the study compared PCR to antigen tests, or rapid tests, which are not the same type of tests.
“It still tells you that the virus is probably there before in the nose, so I wouldn’t be surprised if that ends up being true. But how that translates to home testing, we have to be careful,” she said.
Miller said while she wouldn’t be surprised if the omicron actually showed up in the throat before it did in the nose, that hard data has yet to be presented.
“I’ve been critical of some of the actions the FDA has taken in the past, but I would advise against using these off-label tests until we have evidence,” she said.
Matt Binnicker, director of clinical virology at the Mayo Clinic, said the fact that positivity rates are skyrocketing in the United States is a testament to how well Covid testing is working.
“If there was something about omicron that made it present in the throat but not in the nasal passages, we wouldn’t see positivity rates spike like they have over the past three weeks,” did he declare. “Before we start going to Twitter and saying, ‘Hey, my friend got a throat swab, so everyone should,’ we should collect the data.”
According to Miller, it’s best to get a rapid test on day one, day two, and day three of symptoms if you test negative but your symptoms persist. You also need to isolate yourself.
“If you have symptoms, you have Covid until proven otherwise,” she said.
Binnicker recommends testing three to four days after being exposed to Covid, even if you don’t have symptoms.