As her family prepared to gather for Christmas in Pennington, N.J., Rona MacInnes was determined to protect her elderly mother.
MacInnes hoped the tests would catch the coronaviruses that her son might bring home. The college junior took six rapid tests before the holiday and all of them returned negative results. After he had spent time with his grandmother, it would become clear that he had been exposed to the same disease all the time. He got a positive result from the first lab-based test he was able to book a few days after Christmas.
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MacInnes was frightened by the result and worried about her mother. The family booked an appointment to get a test for her mother that came back negative.
MacInnes said that none of them have developed symptoms.
The promise of at- home tests to tell people whether they are infectious has been undermined by anecdotal reports like MacInnes's, but by preliminary data that suggest some of the rapid tests may be less sensitive to the now-dominant omicron variant. People are urged to take the tests multiple times because studies suggest they detect infections in two to five days after exposure to people with high viral loads. They are not completely safe. For those who have taken the time to find out if their sore throat and sniffle is related to covid-19, the results are often disappointing.
A New York woman who relied on negative rapid test results to go out with her friends on New Year's Eve only to get a positive test result later said she believes the at- home tests offer a false sense of security.
The Food and Drug Administration acknowledged the issue on December 28, noting that early data suggests that the test may have reduced sensitivity. A small preprint study that has not yet been peer-reviewed found that the rapid tests failed to detect the virus on day one after 30 people were exposed to it in New York and San Francisco. In 28 of the cases, the patients had high levels of the virus that made them infectious. Several authors of the study serve on the board of directors of a test protocol affiliated with the Yale School of Public Health.
A study done in California found that Abbott's rapid test performed well in detecting infections caused by the omicron variant as well as those caused by other variations, especially among people with symptoms. The tests failed to detect 10% of lab-confirmed positive cases among people who may have been tested very early in their infections.
The researchers said that their data supports the recommendation for repeat rapid antigen testing for people at risk for covid-19.
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Public health experts say that at- home tests were never expected to be as sensitive as the tests performed in a lab or clinic because of the different ways they work.
The tests use a technique called a polymerase chain reaction. They're considered the gold standard for detecting infections, but it can take hours to deliver results and cost more than $150 without insurance.
Most people can administer rapid tests at home. They can return results in as little as 15 minutes by detecting the antigens on the surface of the virus. Since rapid tests don't make the virus bigger, a person needs to have enough antigens in their body to return a positive result.
The good news is that two new rapid tests coming to market later this month work well in detecting omicron, the now-dominant variant. The FDA granted emergency use authorizations for the tests in late December.
"Help is on the way", said a doctor and engineer who runs a lab for evaluating the performance of rapid tests at the National Institutes of Health. The two new tests performed well.
The government enlisted the Atlanta Center for Microsystems to evaluate coronaviruses tests in March 2020. He has no affiliation with either of them.
Some are better at detecting omicron than others, and each test uses lab-made antibodies that act like glue to "capture" and detect virus. He said his lab has been evaluating the existing tests to see how they stack up against the omicron variant.
"These two new tests have very good antibodies that stick to the virus, likely better than the antibodies of other tests on the market."
Consumers will be able to purchase tests from late January, according to a spokeswoman. It is too early to say when the tests will be in stores, but production is already ramping up. The nation's supply of rapid tests is expected to be boosted by tens of millions of at- home test kits each month.
When the omicron variant first arrived in the United States, he and his colleagues used inactivated virus samples to test all of the rapid tests on the market. All did well. Some of the tests were less sensitive to the variant when they began evaluating them.
There could be a lot of reasons for this.
Some substrains of the variant may produce less of the antigen that the tests are designed to detect. Differences in patients' vaccination status, severity of infections, and how long they've had symptoms may affect how well the tests work.
The early findings are still theoretical. We need to do more rigorous testing.
There is debate over whether people should use throat or nasal samples for their tests because of the presence of Omicron in different parts of the body. The FDA says the rapid tests were not designed for them.
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More reliable rapid tests are needed for people who want to return to their pre-pandemic lives.
A New York City woman took a rapid test on Wednesday after a painful headaches and dry cough spurred her to do so after a New Year's Eve spent with four friends. The test came back negative, but she decided to get a test on Thursday.
The test came back positive.
The woman, who spoke on the condition of anonymity because she is in interviews to change jobs, said that everyone thought that was the key to freedom. If people are getting false negatives, they're adding to the spread.
A single negative rapid test result doesn't preclude that an individual is infectious because the levels of the virus in a person's body change over time. The tests are expensive and still in short supply, so they advise you to use them at least two times over the course of several days. The omicron variant appears to make people less likely to return positive results during the first day or two of symptoms.
William Schaffner, professor of infectious diseases and preventive medicine at the University of Tennessee, said that some people turn positive after a few days. All of this leads to a lot of confusion.
The tests were never designed to be used as a "Get Out of Jail Free card" because of the uncertainty.
Schaffner said that false positives from rapid tests are less likely. "If you use any test in a population where the risk of having a true positive is very, very, very low, you can get false positive results just by chance alone, because no test is perfect," he said.
A positive result from a rapid test should always be treated as a positive, according to many experts.
The omicron variant causes infections to move faster than the other ones, according to the medical engineer at the Emory University. A positive result on a rapid test followed by a negative result on a test for the same disease may mean that a patient is not infectious, but stopped producing the disease by the time of the second test, he said.
"If the test says you're positive, then you're likely infectious, and you're probably positive too," he said.
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