COVID-19: The new saliva test promises to be cheaper and faster

Dr B. J. C. Perera

Specialist Consultant Paediatrician

Extensive and rapid result oriented testing to detect coronavirus infections is a vital key during the on-going pandemic. Detecting an infection early would help to contain the spread of the virus and help save lives. Many countries around the world have been exasperated over testing shortages and delays for a considerable time.

A new saliva-based test for COVID-19 could offer a fast and inexpensive solution to millions of people. This new laboratory diagnostic test has been developed by researchers at the Yale School of Public Health in the USA. In a paper published on 04th August 2020 in the preprint server medRxiv, a team from Yale documented the new tool called ‘SalivaDirect’. Another team, comprising many of the same researchers, had earlier this year detailed that saliva could be collected in any sterile container and that it remained mostly stable, without the need for special tubes or preservatives. 

Until now, detecting the novel coronavirus SARS-CoV-2 involved the reverse transcription-polymerase chain reaction test. This “RT-PCR” test is conducted by collecting a sample from the back of a person’s nose or mouth. While effective, the nasopharyngeal swabbing is unpleasant and the test is not cheap. There is also a limit to the amount of COVID-19 testing that can be done through this method.

This is where the new ‘SalivaDirect test’ could be a real game-changer as it promises to be faster, less expensive and more flexible. With saliva being quick and easy to collect, this test could indeed be a significant advance in COVID-19 diagnostics. Up to now, the results have shown that SalivaDirect is highly sensitive and produces similar results as nasopharyngeal swabbing. Now, further tests are being conducted to see if the method can be successful as a test for asymptomatic individuals, too. Compared to nasopharyngeal swabs, researchers found a “high agreement” of more than 94 per cent in detecting true positives between the two methods.

The SalivaDirect test doesn’t require a special swab or collection device. It can also be used with reagents from various vendors. The researchers had simplified the test so that it only costs a couple of dollars. The cost per sample could be as low as $1.29 to a high of $4.37, with the addition of a saliva collection aids.

A key step in the traditional COVID-19 testing includes extracting the virus’s RNA after the sample is collected before it can be detected by sensitive PCR-based methods. SalivaDirect removes the extraction step and replaces it with something very simple. An enzyme is added and the mixture is heated up. This process removes the most expensive step which is the most time consuming one which requires the most skill as well. The new test can run approximately 90 samples in fewer than three hours and has the potential to scale higher in bigger laboratories having automation. What’s even more encouraging is that Yale is offering SalivaDirect’s protocol open source. This means that researchers around the world can take and modify the method for use in their own labs depending on the resources they have.

Moreover, the saliva-based test is safer, too. In the traditional method, when the swab is inserted into the back of the throat, it often leads to a cough or a sneeze. Thus, there’s always a risk of the discharge of droplets from the person carrying the virus. With SalivaDirect, that risk is minimized as only the saliva will be collected. It can be further reduced if the sample is self-collected under the supervision of a healthcare professional. Thus far, the only condition with SalivaDirect is that the sample collected should be clear liquid saliva. This effectively means that the technique may not be suitable for hospitalized COVID-19 patients because their saliva samples may contain blood or mucus that can affect the final reading. Barring this, SalivaDirect does seem to be a good, low-cost, and effective method for rapid detection of COVID-19.  

The United States of America Food and Drug Administration (FDA) has now given Emergency Use Authorization to SalivaDirect. The low-cost and non-invasive procedure requires minimal processing and retains much of the accuracy of traditional nasopharyngeal swabs. FDA Commissioner Stephen Hahn says in a press release announcing the emergency use authorization, “Providing this type of flexibility for processing saliva samples to test for COVID-19 infection is ground-breaking in terms of efficiency and avoiding shortages of crucial test components like reagents”.

SalivaDirect has already been used voluntarily by several teams of professional basketball players. People such as coaches, staff, and players from both the National Basketball Association (NBA) and the National Basketball Players Association (NBPA) of the United States of America began voluntarily using the test in June, and their participation was central in gaining FDA Emergency Use Authorization.