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Study Finds Performance Declined in Some At-Home COVID-19 Tests During Omicron Surge

NEW YORK – A Dutch study from the BMJ published on Wednesday found that the performance of three widely used at-home antigen tests for COVID-19 declined during the Omicron surge of the pandemic. 

Results from Acon Laboratories' Flowflex COVID-19 Antigen Home Test, MP Biomedicals' Rapid SARS-CoV-2 Antigen Test Card (referred to as MPBio in the paper), and Siemens Healthineers' Clinitest Rapid COVID-19 Antigen Test were studied in 6,497 patients with COVID-19 symptoms who were tested at three public health service sites in the Netherlands between mid-December and early February. 

All of the study's participants had a reference PCR test taken at the site and then were given a rapid antigen test to perform at home using either nasal self-sampling in Phase 1 of the study or combined oropharyngeal and nasal self-sampling in Phase 2. The Flowflex test wasn't used for oropharyngeal sampling because the swab provided was not suitable, the researchers said.

According to the study, the sensitivities of all three tests declined during Phase 1: Flowflex dropped from 87 percent to 81 percent, MPBio dropped from 80 percent to 73 percent, and Clinitest declined from 83 percent to 70 percent. The researchers noted that the Clinitest decline was the only statistically significant one. 

However, when a throat sample was added, the sensitivity of both the MPBio test and the Clinitest increased, to 83 percent and 77 percent, respectively. The researchers noted that only the MPBio sample used with both throat and nasal self-sampling combined met the World Health Organization's standards for rapid antigen tests in patients with symptoms: at least 80 percent sensitivity and at least 97 percent specificity.

The authors proposed several potential reasons for lower sensitivities due to Omicron, such as mutations in the nucleocapsid protein that could have affected the binding efficiency of antibodies used in the tests or a larger proportion of people may have experienced a SARS-CoV-2 infection, which could have affected the tests' performance.

The researchers noted that there were limitations in the study, including the fact that nasal and combined throat and nasal self-sampling weren't conducted during the same time periods, so the proportion of Omicron infections could have been higher during the combined sampling period. 

They also said that there were slight differences in sampling methods for the PCR reference test, which could have affected the results. That being said, the Omicron variant was present in at least 90 percent of the samples for both periods, so the authors said they didn't think the sampling method of the reference test substantially impacted the results.

The researchers recommended that rapid antigen test manufacturers consider extending their instructions for use to include combined oropharyngeal and nasal self-sampling. The authors said that, based on the study's findings, people with COVID-19 symptoms who receive a positive antigen test result can rely on it regardless of variant or sampling method without a need for confirmatory testing, while people with a negative result should still "adhere to general preventive measures because a false negative result cannot be ruled out."

The BMJ also published an accompanying editorial from BMJ Research Editor Timothy Feeney and Charles Poole, an associate professor of epidemiology from the University of North Carolina at Chapel Hill, which determined that while people are capable of doing their own sampling, "the real world performance of antigen tests remains highly variable." The editorial also noted that it is "unclear how many test kits are capable of expanded use" to include oropharyngeal sampling, and that "serial testing could be a more workable change to testing protocols." 

The editorial's authors added, "In the UK and the US, policies governing use of tests to enable a return to normal activities are confusing, poorly explained, and frequently change." The "simple guidance" given by these policies is "inconsistent" with this study's findings, and they noted that "a single negative test result cannot be interpreted in a vacuum."