What do we need to do at home – smear nose or throat swabs? Do rapid tests detect omicron at all? PCR are the only results we can trust right now?
Guidance on how to approach testing in the omicron age seems to be evolving day by day. Recent real research that followed 30 topics Those likely exposed to omicron found that saliva PCR tests could detect cases of Covid-19 three days before rapid antigen tests that use nasal swabs. These findings, which have not been peer-reviewed, follow the FDA’s statement in late December that despite detecting omicron, rapid antigen tests may now have “reduced sensitivity… “But that doesn’t mean rapid tests aren’t playing a key role in our future response to the pandemic.
All of this is confusing the public, which has been pulled in several directions during the pandemic when it comes to recommendation and testing. Long delays in PCR test results, a shortage of rapid tests at home, and waiting for more accurate scientific evidence on the omicron variant all make it difficult to figure out when and how to get tested. Nonetheless, public health experts say that as more cases grow, rapid tests will become an increasingly important tool for diagnosing Covid-19 and reducing its spread.
So you might be wondering: what’s the point if rapid tests are not as accurate as PCR tests? Well, rapid antigen tests that look for a specific protein from the Covid-19 virus remain extremely effective in confirming positive cases. Simply put, if you test positive for a rapid test, you almost certainly have Covid-19. If you test negative, in some cases you can still get a positive PCR test, which is much more sensitive because it checks for genetic evidence of the virus. Rapid tests may fail to detect positive cases in people who have been vaccinated or recently recovered from Covid-19, as they may produce less of the virus, one Recode expert said.
Rapid tests can also identify a positive case faster than laboratories that process PCR tests, as it can take days for them to share results with patients, especially during large waves of infection. Perhaps more importantly, quick tests can indicate if someone is contagious enough to spread the virus to others, which is what worries many people the most.
“Given that rapid antigen testing is often the most feasible or affordable option for many, we do not want the ideal to be the enemy of the good,” said Joshua Michaud, deputy director for global health policy at the Kaiser Family Foundation, told Recode. He explained that every case of Covid-19 detected by someone who can take a rapid antigen test but not a PCR test is a public health victory.
More frequent rapid tests also make them more effective. Most rapid home testing kits are designed to run within two days, so kits usually include two tests. Since each test is a snapshot of the moment it was taken, multiple tests can help reduce the chance of a false negative result.
Of course, this all assumes that you can get a quick test. In the weeks after omicron began to spread, rapid tests were incredibly difficult to find in parts of the country. These tests are not available because neither the test makers nor the Biden administration expected record levels of Covid-19 cases, which has boosted the demand for rapid tests. To counter the deficit, the White House plans to purchase and distribute 500 million free rapid tests in the coming weeks. When that happens, these tests can help identify more positive cases and reduce the number of people infected with Covid-19.
How accurate are rapid tests when it comes to omicron?
The accuracy of the rapid test depends on how often you test yourself and whether you want to identify a Covid-19 infection or measure your infectivity. But if you have a positive rapid test result, you must trust the result, assume that you are contagious, and isolate yourself for at least five days… If you test positive again after five days, the CDC recommends isolation for an additional five days.
However, rapid tests are not perfect. Research shows that antigen tests are less accurate than PCR tests – this has been the case since the beginning of the pandemic. PCR tests are processed in a laboratory where sophisticated equipment can identify and amplify even the smallest genetic traits of the virus that causes Covid-19. These tests are so accurate that patients may actually test positive for several weeks after they have recovered and no longer infectious… Meanwhile, rapid test results can vary depending on how much virus is in the patient’s nose at the time the sample is taken and how far they have progressed in their infection.
Scientists explain the difference between rapid tests and PCR tests in two ways: specificity, which reflects the rate of false positive test results, and sensitivity, which reflects the rate of false negative test results. Both PCR and rapid tests are highly specific, which means that their positive results are highly credible. But while PCR tests tend to have near-perfect sensitivity, rapid antigen tests usually have a sensitivity of 80 to 90 percent. This means that rapid tests tend to give more false negative results than PCR tests.
Omicron makes testing even more challenging. According to early research by the FDA and others, the sensitivity of rapid tests may be even lower for omicron cases. Another problem is that the omicron can multiply more in the throat than in the lungsand Covid-19 may take longer to detect in nasal specimens, even if someone has symptoms. It’s possible that vaccinated people and people who have recently recovered from Covid-19 notice more false negative rapid test results because, overall, they tend to produce less virus.
“Home tests are most effective when a person has a high viral load, that is, at a time when the person is more likely to transmit the virus,” Pablo Penalosa-McMaster, a viral immunologist at Northwestern University School of Medicine, told Recode. Home tests are still able to detect omicron infections because they target the part of the virus that does not mutate as much. ”
Separate studies from both UK Health Safety Agency and researchers in Australia found that antigen tests were as sensitive to the omicron variant as to earlier strains of Covid-19. Again, the FDA still recommends rapid tests to diagnose positive cases, and the test makers say they have confidence in their products’ ability to detect omicron. Still early research indicates that saliva tests can detect Covid-19 faster, currently most PCR tests and all available rapid home tests that are FDA-approved for emergency use use nasal specimens.
How to use rapid tests in non-ideal conditions
Which brings us back to the question of whether to put nose swabs down the throat. There is evidence that saliva samples may be a faster indicator of Covid-19 cases, but that doesn’t mean you should stop following the instructions that came with your test kit. The FDA says people should not use rapid antigen tests for mouth swabs. Some experts say you might still think about it and point out that other countries, including the UK, have approved rapid antigen tests that use throat swabs and has issued very detailed instructions on how to do this.
“I personally take throat and nose swabs to get the most sensitivity when I use over-the-counter tests at home,” Michael Mina, a Harvard epidemiologist, said at a press conference on Thursday. “There are risks associated with this, but biology tells us they may be more sensitive earlier.”
But now the problem with rapid test kits isn’t that people get nasal swabs, but how often they get nasal swabs. One test can miss a case of Covid-19 and give a false negative, but running two tests over a period of 24 to 36 hours reduces this risk. The more rapid tests you take, the more you will reduce your chances of a false negative, and the more times you test negative within a few days, the more confidence you will have that you are not spreading Covid-19.
However, the biggest problem right now is that rapid tests are expensive and difficult to find. Pharmacies have limited the number of test kits that people can buy, and many are completely out of print. A single test can also cost over $ 10, which means that it quickly becomes expensive to test yourself regularly. The opportunists even saved up tests and gouges prices, which exacerbated the deficit.
If you don’t have enough tests to test yourself regularly, it’s best to test yourself right before you see vulnerable people, says Mara Aspinall, a professor who heads the Arizona diagnostic community and a board member of test maker Orasure, told Recode. “I’m heading for a vulnerable person [or] I am going to a medical facility, and therefore I need to take a test right before that. ”
The best test suite right now is the test you can get (Wired has handy list currently available brands). If you are planning to travel somewhere and do not want to spread the virus, you should take one rapid test the day before the trip, and the second immediately before the trip. If you only have one rapid test, take it right before meeting people.
Self-testing should become easier as faster tests become available. In addition to the 500 million free rapid tests the White House will distribute. starting at the end of this monthPeople with private insurance will also be able to get reimbursed for purchases for express tests. Starting next week… You should also check with your local health department as they can distribute free tests.
While the rapid test situation is still not ideal, there are other strategies we can use to protect ourselves and others from Covid-19, such as getting vaccinated, boosted vaccinations, and wearing a mask. And if you manage to find some quick tests, take them. They can just come in handy, especially if used correctly.
Correction, Jan 7, 10:30 am: In an earlier version of this story, false results were skewed in one case, which may appear more often with rapid tests for Covid-19 among vaccinated people and people who are immune from recent infection. False results are false negatives, not false positives.