Home Tests Detect the New COVID Variant, But May Take Longer

Jan. 23, 2024 – You’ve sewage nan symptoms, but your trial for COVID-19 isn't positive. You’re not alone. 

JN.1, nan now-dominant version that accounts for nearly 86% of each circulating SARS-CoV-2 strains, whitethorn return longer to show a affirmative consequence connected home antigen tests.

Some infectious illness doctors and patients person reported that tests taken days aft symptoms look move up negative, past a mates of days later are positive. 

It’s triggered uneasiness astir nan worth of nan tests. “Are nan at-home tests capable to observe JN.1?” tweeted 1 personification connected X, formerly known arsenic Twitter, echoing concerns of others connected societal media.

Before blaming nan tests for losing effectiveness -- aliases nan version for being excessively wily to beryllium detected -- infectious illness experts connection different explanation: our smarter-than-in-2020 immune systems. They besides constituent to a study published successful September that recovered galore patients aren’t getting a affirmative trial until 4 days aft infection. 

Our immune systems are getting stronger, said Peter Chin-Hong, MD, an infectious illness master and professor of medicine astatine University of California, San Francisco, School of Medicine. As nan pandemic has gone connected and overmuch of nan organization has gotten earthy infections, vaccines, aliases both, “we are getting alerted earlier that nan force is successful nan body. It’s much related to clip alternatively than to nan variant,” he said.

That intends we whitethorn consciousness sick earlier from COVID now compared to earlier successful nan pandemic. 

In March 2020, everyone was naive immunologically, he said, and “it took immoderate clip for nan assemblage to admit nan virus.” Now,  just a spot of microorganism whitethorn trigger an siren by nan immune system, pinch symptoms showing up quickly. These days, he said, “you whitethorn now consciousness sick astatine time zero alternatively of time 5.” However, erstwhile you trial wrong nan first fewer days, location whitethorn not beryllium a very precocious level of virus, truthful nan location test, little meticulous than nan less-available PCR tests, astir apt won’t beryllium positive. 

Chin-Hong says he doesn’t think, however, that early variants will agelong retired that lag clip overmuch further.

‘New Normal’ Not Brand New

These “delayed positives,” arsenic others word them, person occurred pinch different variants. As nan organization has gained immunity to owed to earthy infections, vaccinations, aliases both, nan viral load does highest later, explaining nan lag clip that tin hap connected location trial results, according to nan September study successful nan diary Clinical Infectious Diseases.

“In our study we observed that successful a highly immune big organization (91% had a history of vaccination, earthy infection, aliases both), concentrations of viral RNA and antigen successful nasal swab samples were highest astir nan 4th time of symptoms,” said interrogator Nira Pollock, MD, PhD, subordinate professor of pathology and medicine astatine Harvard Medical School.

For that reason, nan sensitivity of location tests would beryllium expected to beryllium highest astir nan 4th time of symptoms, she said, though galore group pinch symptoms mightiness trial affirmative earlier. 

In nan study, Pollock and her colleagues evaluated nasal swab samples from 348 group who had tested affirmative by PCR testing for COVID, measuring nan concentrations successful nan sample and past estimating nan expected sensitivity to location testing. The tests were done from April 2022 to April 2023, good earlier nan JN.1 version was first detected successful nan U.S. in September 2023. 

Handling nan ‘New Normal’

How to grip nan lag time?

The CDC advises testing instantly if you person symptoms. If a location trial is negative, retest aft 48 hours aliases get a PCR test. It recommends waiting 5 days aft vulnerability to trial if you don’t person symptoms, past either trial astatine location again successful 48 hours if your first trial was negative, aliases get a PCR test. Those who don’t get nan PCR should repetition nan location antigen trial a 3rd clip aft different 48 hours. Keep successful mind, however, that PCR tests done astatine a laboratory are nary longer free.

The investigation shouldn’t discourage testing, Pollock said. 

“People should proceed to trial arsenic soon arsenic they person symptoms,” she said. If they trial positive, that accusation is very important for making curen and different decisions, she said. The cardinal is that group request to cognize that 1 trial is not enough. But she acknowledged that repetition testing is some challenging and costly.

According to Chin-Hong, nan testing decisions are individual and could dangle connected a person’s entree to tests. “If you person constricted tests, I would astir apt not cheque instantly [after symptoms occur] but hold and deterioration a mask.” But he acknowledged that some, including older adults and anyone who is immunocompromised, whitethorn want to trial earlier and much often, arsenic they want to cognize their position earlier alternatively than later.

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