Testing has once again emerged as a source of frustration as the coronavirus disease (Covid-19) pandemic continues into its fifth year.
Tests were often hard to come by in early 2020, but the plethora of cheap, rapid kits now in grocery stores and home medicine cabinets has raised new concerns that they may not be effective. There is.
“People who are told they didn’t get a positive result on a rapid antigen test are often the ones who come to me because they’re frustrated,” said Dr. Michael Mina, an immunologist and epidemiologist.
In fact, the test works just as it did when it was first published.
What has changed is our body’s response to the coronavirus, leading many people to get tested too early, says the author, who helped implement the U.S. government’s at-home testing and treatment program a year ago (in 2023). said the chief scientific officer of digital healthcare company eMed LLC.
your body is a test kit
In 2020, loss of smell and taste, fatigue, and dry cough signal the onset of Covid-19, usually occurring one week after the SARS-CoV-2 virus enters the body. did.
“The first symptoms appeared after the virus tore you apart.”
Since then, through multiple vaccinations and natural infections, most people have been “educated in immunology,” Dr. Mina says.
Growing immune wall allows the body to recognize the SARS-CoV-2 virus faster and suppress it more effectively, even as the virus has spawned dozens of new variants became.
He said stuffy nose, fever and other early signs of viral illness can appear within one to two days of infection during the “prodromal phase,” which occurs before full symptoms of the disease develop.
“It’s just our immune system saying, ‘Hey, we’re starting to recognize something here,'” he says.
Some scientists believe that the incubation period for coronaviruses has shortened over time because the immune system has responded faster.
However, Mina said the virus’ growth dynamics have remained largely unchanged since 2020.
“It takes the same amount of time for a virus to go from, say, 10 particles to 10 million particles.”
In 2020, health officials recommended waiting four or five days after getting coronavirus to get tested, reflecting when the amount of virus in the upper respiratory tract is near its peak and easily detectable.
However, the relative ease of developing prodromal symptoms and home testing has allowed people to screen for COVID-19 sooner.
“Many people are trying to get tested within 24 to 48 hours of being infected,” said Dr Mina, a former assistant professor of epidemiology, immunology and infectious diseases at Harvard University’s TH Chan School of Public Health in the US.
“And just like in 2020, the virus is not yet replicating to high levels in the nose.
“It actually takes four, five, six days.”
He says the “educated” immune system provides a kind of built-in rapid test.
Instead of showing a positive result with a new line on the test strip, the signal is accompanied by congestion and fever.
“Once the ‘immune test’ has already started showing something exists, we may have to wait another day or two before we can perform a confirmatory rapid antigen test,” he says. .
Negative means low risk
Research into household transmission patterns early in the pandemic showed that infected people were most likely to spread the virus four to six days after being exposed.
The window of transmissibility hasn’t changed much since then, Dr. Mina says.
People who receive a negative rapid test two days after being infected with the coronavirus remain at low risk of spreading the coronavirus.
“Is it possible that you could infect your spouse or someone very close to you on the second day? Probably,” he says.
“But is it possible for you to be a super spreader and test negative? Probably not.”
On the other hand, a positive test indicates that the virus is present in large quantities and there is a risk of infecting others.
Dr. Mina recommends swabbing both the throat and mouth to increase the sensitivity of the rapid test, as virus levels in both areas can vary from person to person.
Also, the coronavirus is most likely to survive at 37 degrees Celsius, making the throat a better environment to live in than the nose.
Even if you develop mild symptoms after being infected with the coronavirus and a rapid test remains negative for several days, this does not necessarily mean that you have escaped infection, nor is there anything wrong with the swab collection method or test. , he says.
Rather, it may mean that the person’s “educated” immune system has successfully stopped the virus from reaching levels detectable by rapid antigen tests.
The threshold is about 100,000 copies per milliliter, a fraction of the 1 billion to 1 trillion copies per milliliter that an individual can have at peak infectivity, he says.
As people’s immunity increases, it is more likely that more people will not test positive on a rapid test even if they become ill with the coronavirus.
“I hope all tests are false negatives, because that represents a victory for immunity,” he says.
“That means your immune system is doing what it’s supposed to do.”
Still, Dr. Mina cautions that even if the virus is suppressed in the respiratory tract, it can multiply elsewhere in the body, such as in the gastrointestinal (GI) tract.
“If you really think you’ve been infected and feel you’re having gastrointestinal symptoms, treatment may be appropriate. Even if you don’t test positive, it makes sense to give paxlobid. “There may be,” he says.
“The test is only as accurate as the sample, and the accuracy of the sample is determined by where the virus is in the body.” – Written by Jason Gale/Bloomberg News/Tribune News Service