COVID-19 tests became a common tool for managing the pandemic. As the SARS-CoV-2 virus continues to change, new variants have emerged. This raises questions about whether existing tests remain reliable for detecting new variants.
How COVID-19 Tests Identify the Virus
COVID-19 diagnostic tests identify SARS-CoV-2 virus components in a sample. Two main types are widely used: rapid antigen tests and PCR tests. Rapid antigen tests detect specific viral proteins, known as antigens.
PCR tests, also known as molecular tests, look for the virus’s genetic material (RNA). They amplify genetic segments, making even small traces detectable. PCR tests are generally more sensitive than antigen tests.
Why Viral Changes Affect Test Performance
Viruses, including SARS-CoV-2, constantly undergo genetic changes as they replicate and spread through populations. These changes are called mutations, and a collection of mutations can lead to the emergence of new viral variants. While many mutations have little to no impact on the virus’s characteristics, some can alter how easily it spreads, the severity of the illness it causes, or how effectively diagnostic tests can detect it.
Mutations can specifically affect test performance if they occur in the particular parts of the virus that a test is designed to target. For instance, if a test looks for a certain protein or genetic sequence, and that specific region mutates significantly, the test’s ability to “recognize” the virus might be reduced. However, not all mutations will compromise test accuracy; only those in the targeted detection areas pose a potential challenge. Scientists monitor these changes to understand their implications for existing diagnostic tools.
Antigen and PCR Tests and Variants
The impact of viral variants differs between antigen and PCR tests due to their distinct detection mechanisms. Antigen tests primarily target specific viral proteins, such as the nucleocapsid protein, which is abundant in infected individuals. If mutations occur in these targeted proteins, an antigen test’s sensitivity might decrease, potentially leading to false negative results, especially with low viral loads. Despite this, research indicates that the viral protein detected by most antigen tests has remained relatively stable, allowing them to perform well against recent variants.
PCR tests, which detect the virus’s genetic material, are generally more robust against single mutations because they often target multiple regions of the viral genome. If a mutation affects one target region, the test can still detect the virus using other unaffected regions. However, a significant alteration across multiple target areas could theoretically impact PCR test performance. Health authorities like the CDC and WHO continuously monitor variants and assess the ongoing effectiveness of both test types, generally affirming their continued utility for most current variants.
What to Do After Testing
Regardless of the test result, symptoms remain an important indicator of illness. If you experience COVID-19 symptoms, it is advisable to test immediately. A positive test result typically means you have COVID-19 and should follow public health guidelines regarding isolation to prevent further spread.
A negative rapid antigen test result does not always rule out an infection, particularly early in the course of illness or if viral load is low. If you test negative but have symptoms, or if you were exposed to someone with COVID-19, it is recommended to retest. For symptomatic individuals, retesting 48 hours after an initial negative result is often advised. If you have concerns about your test results or severe symptoms, consulting a healthcare professional is important for guidance and potential further testing.