The COVID-19 pandemic has brought widespread testing for the SARS-CoV-2 virus to the forefront. As new variants emerge, questions arise regarding which tests can accurately detect specific strains. One of the most common rapid antigen tests is the BinaxNOW COVID-19 Antigen Self Test made by Abbott. With the rise of the highly transmissible Delta variant, many are wondering if this test can identify Delta infections.
How the BinaxNOW test works
The BinaxNOW test is an antigen test that detects proteins from the SARS-CoV-2 virus through a nasal swab sample. It works by using antibodies that bind to specific viral proteins. When the viral proteins are present in the sample, they attach to the antibodies on the test strip, leading to the appearance of a colored line. This qualitative test provides results in 15 minutes without the need to send the sample to a lab.
The test was designed to detect both active and early infection by targeting the nucleocapsid protein. This is a protein found within the virus but not on its surface. Antibody tests, on the other hand, look for antibodies created by the immune system in response to infection. Since nucleocapsid proteins are present before the body mounts an antibody response, the BinaxNOW can detect the virus earlier in the course of infection.
BinaxNOW accuracy
The BinaxNOW test has demonstrated very high specificity, meaning it almost never provides a false positive result. In clinical studies submitted to the FDA, it showed 100% specificity. However, its sensitivity has been more variable. Sensitivity refers to the ability to correctly identify positive cases. In these studies, the test showed 80.0-84.6% sensitivity within the first seven days of symptom onset.
Real-world evidence reflects these findings. In a study of asymptomatic testing at two universities using mainly the BinaxNOW test, only 64% of cases were detected. Meanwhile, a study in Washington state found 79% sensitivity in symptomatic individuals. Accuracy has been shown to be higher in those with higher viral loads around the time of symptom onset. Accuracy may decrease as time from exposure increases.
Does BinaxNOW detect the Delta variant?
The BinaxNOW test was designed and tested prior to the emergence of the Delta variant. However, since it targets the nucleocapsid protein rather than the spike protein, it is expected to detect all known variants. The Delta variant has the same nucleocapsid protein as the original SARS-CoV-2 virus first identified in Wuhan in 2019. Several real-world evaluations have borne out this hypothesis.
CDC evaluation
In June 2021 as Delta was rising to prominence, the CDC evaluated the ability of four common antigen tests, including BinaxNOW, to detect live Delta virus in cultured samples. They found the following:
Test | Detected Delta in culture? |
---|---|
BinaxNOW | Yes |
QuickVue | Yes |
BD Veritor | Yes |
Quidel Sofia | Yes |
All the tests successfully detected the Delta variant viral proteins. This indicates they can be relied upon to identify Delta infections just as accurately as other strains.
Real-world data
Real-world data has also demonstrated the ability of antigen tests like BinaxNOW to detect Delta:
- A study in Utah found that the BinaxNOW identified 100% of samples that were positive for Delta by PCR.
- Research from Singapore showed no difference in detection of Delta compared to other strains with either PCR or antigen rapid tests.
- The UK Health Security Agency has reported similar sensitivity of lateral flow tests like BinaxNOW to Delta as to other variants.
Together, this data confirms that the BinaxNOW and similar antigen tests reliably detect Delta with equal sensitivity as previous variants.
Pros and cons of BinaxNOW for Delta
Here are some key advantages and limitations of using the BinaxNOW to test for Delta infections:
Pros:
- Results within 15 minutes allow for quick public health decision making
- Self-administration makes frequent community screening feasible
- Low cost and widespread availability
- Allows early detection of Delta prior to symptoms
- Requires less technical expertise than PCR tests
Cons:
- Lower sensitivity than PCR, especially later in infection
- Does not indicate which variant caused infection
- Still requires a nasal swab sample
- Cannot be used to clinically rule out COVID-19 if negative
- Risk of false negatives requires confirmatory PCR test
Overall, the BinaxNOW can serve as a useful screening tool for Delta infections due to its reasonable accuracy, quick results, and accessibility. However, PCR testing is still necessary for definitive diagnosis of individual cases.
Using BinaxNOW to screen for Delta
Several key settings may benefit from strategic implementation of BinaxNOW testing to detect Delta cases:
Schools
Frequent rapid antigen testing of all students and staff can identify asymptomatic Delta cases and trigger containment measures like isolation, contact tracing, and quarantine. This layer of screening can limit transmission chains within schools.
Workplaces
Worksites that have hesitated to mandate vaccination may implement policies requiring unvaccinated employees to test 1-2 times per week. This would identify Delta breakthroughs in vaccinated individuals and new cases in the unvaccinated.
Healthcare facilities
Hospitals and nursing homes can require visitors to have a negative BinaxNOW test from the same day to prevent introduction of Delta from the community. Regular staff testing would also be prudent.
Congregate living sites
Frequent testing in crowded housing facilities such as prisons and shelters can potentially curb Delta outbreaks through early case detection and containment. However, widespread vaccination is likely the most effective strategy in these high-risk settings.
Large events
Proof of a negative test from the past 72 hours can be an entry requirement for conferences, concerts, and other large gatherings. While imperfect, it may reduce seeded Delta cases.
Careful implementation is key, as feasibility, frequency of testing, accessibility, and cost vary between settings. Still, strategic BinaxNOW screening has the potential to mitigate community Delta spread.
Role of BinaxNOW in containing Delta
While vaccines remain the most critical tool against Delta, inexpensive rapid testing fills an important public health gap. The CDC estimates the BinaxNOW detects infection in around 80% of those with symptoms when used serially. With its widespread availability, low cost, and quick results, it provides a practical option for community screening to identify asymptomatic transmission. However, certain factors limit how much it can contain Delta on its own:
- Cannot prevent infection before a positive result
- Frequent false negatives require confirmation by PCR
- Does not prevent post-exposure transmission
- Short window of detection decreases impact of infrequent testing
- Insufficient for diagnosis of individuals due to false negatives
Rapid antigen testing works best when deployed alongside other containment strategies like masking, distancing, ventilation, vaccination, isolation, quarantine, and contact tracing. Still, the BinaxNOW provides an additional tool to meet the testing surge required for Delta screening. It strikes a useful balance between accessibility, speed, cost, and accuracy. Overall, it can play an important role in a comprehensive public health plan, but cannot stand alone against the Delta variant. Vaccination remains the bedrock for defense against emerging strains.
Conclusion
In summary, the BinaxNOW test can reliably detect Delta variant infections, making it useful for frequent, large-scale screening to identify asymptomatic transmission. While it has reasonable accuracy among antigen tests, it does not match PCR and is insufficient to individually diagnose cases. However, strategic implementation for community testing provides an affordable, practical option to curb silent Delta spread. Alongside other layered mitigation measures, widespread BinaxNOW screening has the potential to box in Delta outbreaks, though it cannot contain the variant on its own. But for true protection against evolving SARS-CoV-2 strains, vaccination remains the most critical tool.