Dubai, United Arab Emirates (CNN) – With coronavirus cases rising across the United States, many people are again relying on home tests to guide their decisions about going to work, sending their children to school, and other activities.
The results of many of these tests will be negative, even if one is 100% sure that they have Covid-19.
This led social media users to speculate that rapid tests may have lost their ability to detect some new variants of the coronavirus.
Dr. Michael Mina, an immunologist and epidemiologist, and chief science officer at eMed Healthcare, said: “Every time a new variant appears, I notice the same dialectic of conversation across the “X” platform (formerly Twitter).”
Mina was an early proponent of selling rapid lateral flow tests to the public as a way to help people understand when they became infected, saying, “People who notice this are not crazy. There are reasons why you might test negative even when you have coronavirus.”
But ultimately, the tests can still detect infection, according to Todd Mirzak, who co-led the RADx program at the US National Institutes of Health.
The program was created during the pandemic to develop special tests to quickly detect the Corona virus.
Tests are less affected by new variants
The reason COVID-19 tests can work even when other tools fail, such as vaccines and monoclonal antibodies that have become ineffective over time, is that the vaccines and antibodies target the spike proteins of the virus.
These protrusions are exposed to constant pressure from the environment around them, which causes them to change, and this is something they are already doing.
On the other hand, most rapid tests target the nucleocapsid proteins, or “N protein,” of the coronavirus.
These proteins do not change as much as spinal proteins.
The importance of tests
The US Centers for Disease Control and Control (CDC) recommended that people undergo rapid testing 5 days after a known exposure to the virus.
“If you look at the kinetic properties of viruses,” Mina explained, “it usually takes 3, 4, or 5 days on average for the virus to go from low levels to a level sufficient to be detected by any test.”
Mina confirmed that the matter has not changed, even with the presence of new variables.
Mina explained that the variants copy themselves slightly faster in the body, but within hours, not days, compared to the original virus.
Now that our immune systems recognize the virus, Mina believes they begin to respond more quickly, and therefore, people develop symptoms faster than they used to.
This may prompt them to get tested early to detect their infection before the virus can build enough copies for tests to detect them.
“It’s a bias that occurs as a result of easy access to home tests,” Mina explained.
Repeated testing improves accuracy
For this reason, late last year the US Food and Drug Administration (FDA) issued a safety statement to the public, advising anyone who received a negative result after taking a home test to repeat it within 48 hours.
The advice to repeat the test came from another government-funded study.
Researchers from the University of Massachusetts studied more than 5,000 people who were recruited to find out how successful home tests were in detecting Covid-19 in the real world.
The study was conducted during the winter of 2021 until 2022.
Study participants tested themselves using rapid home tests every 48 hours for 15 days, and also provided samples for polymerase chain reaction (PCR) testing, a more sensitive method of detecting infection.
During the study, the results of PCR tests were positive for 154 people, and symptoms appeared in 57 people, but they did not appear in 97 of them.
Rapid home tests were more accurate in people who had symptoms.
Infection was detected in about 60% of cases when a single test was performed on the first day of infection when the person showed symptoms.
When the rapid test was repeated two days later, the tests detected symptomatic infection in about 90% of cases.
Rapid tests were less useful in people who did not have symptoms.
2023-09-22 08:59:04
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