COVID-19 tests used to be able to detect a positive case within the first 48 hours, but many results are now delayed until four days after symptoms appear, according to the LA Times.
Elizabeth Hudson, DO, regional chief of infectious diseases at Kaiser Permanente's Southern California Medical Group, told the Times the lag is because of accumulated immunity from COVID-19 through vaccinations or infections.
The tests also might be outdated since they're designed for older variants, Peter Chin-Hong, MD, an infectious disease expert at San Francisco's UCSF, told the San Francisco Chronicle. At-home test kits can still detect newer strains — such as JN.1, which accounts for 61.6% of cases as admissions hit a 12-month high — but more virus samples in the nose are required to trigger a positive test result.
People who are symptomatic and contagious but don't take a confirmation test after a few days "could be getting a false sense of security" from the false negative, Dr. Hudson said.
Delayed results could affect the efficacy of Paxlovid, a life-saving COVID-19 drug that works best when used within the first few days of symptom onset. But use of the antiviral has been dragging over the last few months.
The CDC recommends those experiencing COVID-19 symptoms take a second test 48 hours after receiving a negative result. Experts told the Times and the Chronicle that patients should continue testing every day or every other for up to a week.
Dr. Hudson also suggested heading to a medical facility for a PCR test if at-home kits continue to come up negative despite the presence of symptoms.