At-home COVID-19 tests' efficacy

FDA consistently monitors the efficacies of its currently approved tests and, as of Aug. 3, 2023, hasn't listed any as having "reduced performance" for the SARS-CoV-2 omicron variant and subvariants.

NIH has also found that, after analyzing more than 100 rapid antigen test kits throughout the United States on over 300 COVID-19 variants, the vast majority could detect old and new variants alike.

Additionally, research has found that at-home tests perform as well in 2024 as they did earlier in the pandemic when other variants were circulating.

This is because "the virus protein detected by antigen tests has not changed much over the last two years, unlike other parts of the virus that have undergone many mutations," MedicalXpress reports.

However, while the virus hasn't mutated past the point of accurate detection, how viral load presents in our bodies has changed — meaning people may have to adjust the timing of their at-home testing.

When COVID-19 first emerged, an infected person's viral load reached its peak around the time symptoms began. This meant that, if someone used an at-home test on their first or second day of feeling ill, they had a detectable viral load.

Throughout the course of the pandemic, most of the population has generated some sort of immunity through natural infection, vaccination, or both. Now, with some 96% of Americans aged 16 and older having had some level of COVID-19 antibodies in their blood by Q3 of 2022, this prior exposure and immunity has changed when viral loads are detectable, now reaching their peak at days four to five of infection, according to a recent study.

The study estimates that, while a COVID-19 antigen test is only somewhere between 30% and 60% accurate at detecting an infection on someone's first day of symptoms, it's up to 93% accurate by day four.

At the same time, as the pandemic has gone on and many people have been infected with COVID-19 or gotten vaccinated, "we are getting alerted earlier that the enemy is in the body. It's more related to time rather than to the variant," said Peter Chin-Hong, an infectious disease specialist and professor of medicine at the University of California, San Francisco School of Medicine. This means that we may feel sick earlier from COVID-19 now compared to earlier in the pandemic.

But since viral load may not be high during initial symptom onset, testing early at-home could result in "delayed positives."

Handling potential 'delayed positives'

CDC recommends testing as soon as you have symptoms. If an at-home test is negative initially, retest 48 hours later or get a PCR test.

If you don't have symptoms but have been exposed to COVID-19, the agency recommends waiting five days after exposure to test. If that test is negative, retest 48 hours later with an at-home test or seek a PCR test.

"If you have limited tests, I would probably not check immediately [after symptoms occur] but wait and wear a mask," said Chin-Hong. (HHS Administration for Strategic Preparedness & Response, , accessed 9/23; Kelly/Robledo, USA Today, 9/18; CDC National Center for Immunization and Respiratory Diseases, 8/19; Ducharme, TIME, 9/6; Goodman, CNN, 9/18; FDA, 9/5; Hafer et al, MedicalXpress, 3/2; Doheny, WebMD, 1/23)

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