This week, there’s been a lot of buzz about a new saliva-based COVID-19 test developed by researchers at the Yale School of Public Health. The test, called SalivaDirect, was recently granted emergency use authorization by the FDA.
Vault’s COVID-19 test, developed by RUCDR Infinite Biologics and Spectrum Solutions, was the first saliva test granted such authorization by the FDA, and we have long believed that saliva tests are essential tools in this pandemic. Another saliva test on the market is great news when it comes to being able to scale COVID-19 screening nationwide. It’s also exciting and galvanizing to see more research coming forward on the efficacy of saliva tests.
That said, there are some key differences between Yale’s test and Vault’s—beginning with the fact that the Yale test is a screening test, while Vault’s test is a diagnostic test. Specifically, a screening test is used to flag a condition, while a diagnostic test is used to confirm it. Because of this, the standards and bar for confidence for a diagnostic test such as Vault’s are higher across the board. Here’s what this means:
In order to reduce the cost of testing, SalivaDirect was developed using only commonly available chemicals. It also doesn’t extract viral RNA prior to testing. While this eliminates the need for specialized saliva collection devices with preservatives, it also makes SalivaDirect less sensitive than other diagnostic tests—including Vault’s. SalivaDirect has a limit of detection of 600-1200 viral particles per milliliter of saliva, compared to Vault’s detection of as few as 200 particles per milliliter. In other words, Vault’s test can detect the presence of COVID-19 at significantly lower levels, making it better for earlier detection.
Because SalivaDirect is intended for community screening (assessing for population trends and percentages) rather than diagnostic testing (getting the best possible answer for whether an individual is positive or negative), it is less sensitive than Vault’s test. For example, SalivaDirect only looks for the presence of one viral gene—the N gene—rather than the three genes (N, S, ORF1ab) that Vault’s test looks for. When compared with the ThermoFisher TaqPath assay, one of the most commonly used nasal COVID-19 tests currently available, SalivaDirect agreed with ThermoFisher only up to 94% of the time on positive samples, while Vault’s COVID-19 test agreed with ThermoFisher >99% of the time. The false negative rate for SalivaDirect test is around 7%, in contrast with the ~1% rate for Vault’s test. This means that, scientifically, in order to trust the results of the SalivaDirect test, you would have to do two tests, while Vault’s results only require one test for accuracy.
SalivaDirect’s testing protocol is not yet approved for home collection and requires supervision by a healthcare professional, limiting accessibility. Vault’s test is remotely supervised over Zoom, increasing accessibility—all that’s required is an internet connection. Furthermore, because SalivaDirect does not yet have a broad distribution network, rapid turnaround and quality control is not yet in place. In teaming up with RUCDR Infinite Biologics and Spectrum Solutions, Vault’s test includes expedited shipping to the laboratory and quality controlled results within 48-72 hours after the sample’s arrival at the lab.
One of the biggest advantages of the SalivaDirect test is cost. Because it was developed using commonly available chemicals and does not require specialized saliva collection devices, it is likely to cost less than Vault’s test. At present, developers expect labs to charge $10-20 per sample, making it one of the most cost-effective testing tools on the market. That being said, the price doesn’t account for facilities, instrumentation, laboratory data information management, data tracking, controls, front end, back end, sample logistics, and all other costs associated with a CLIA Lab. These all add significantly to the cost of a test.
At the end of the day, the more COVID-19 testing options, the better. But knowing the difference between a highly sensitive and specific diagnostic test and a less sensitive screening tool is crucial in choosing the right test for your needs. While SalivaDirect’s test may be useful for gaining a sense of how quickly or slowly COVID-19 is spreading across a community, if you need accurate results to act upon, and you want to have that information after testing a single sample—in advance of seeing someone vulnerable to infection or to monitor for COVID-19 among your employees—Vault’s test is the way to go.