Offering painless, non-invasive and rapid results, saliva tests have the potential to change the way we live with the coronavirus.
Imagine if you could pop into your local pharmacy on your lunch break, buy a cheap Covid-19 test, spit into a test tube and have the results before you return to your desk. This could soon be a reality, providing a better way to live with the virus while waiting for a vaccine.
The most common test currently used in France is the nasal version of the polymerase chain reaction (PCR) method, which involves inserting a long cotton swab into the patient’s nose. It is carried out without referral or appointment at laboratories across the country – for free if you have the national health card. The queues are often long and the results can take up to five days to arrive.
More than 700,000 nasal swab tests are now carried out each week in France, in line with objectives announced by the government the day after the lockdown ended. The minister of health, Olivier Véran, estimated that France will be able to "carry out one million tests per week if necessary", speaking at a government press conference on August 27.
The nasal swab test is uncomfortable and involves a risk of contaminating the person performing the test. The person being tested often has a rejection reflex, involuntarily coughing, sneezing or even spitting on the healthcare professional holding the swab.
Saliva tests have the advantage of being simpler to perform, less intrusive, with fewer risks – and the results can be processed more quickly.
"Studies are under way to assess the reliability of saliva tests, which could soon be quick and easy," said Véran.
While France is still doing research on the feasibility of widespread saliva testing, this type of test is already being used in Hong Kong and the United States.
More reliable than nasal swabs?
A recent study has found the results of saliva tests may even be more reliable than those from nasal swabs. People might also be more willing to get regular, repeated tests if they do not involve a painful procedure.
When a pupil in France is suspected of having the virus, his or her whole class may be sent home until the Covid-19 test results come back. If the child tests positive, the whole school may be closed. More than 20 schools have already been forced to close across France since reopening just last Tuesday.
With saliva tests, a school nurse could quickly test a child on the premises and, if the illness turns out to be nothing more than a fever or a stomach bug, the school can continue operating normally. The same practices could be applied to offices as well as airports or other transport hubs.
Similar to a pregnancy test
A sample of saliva (one of the main vectors of the virus) is placed in a test tube with reagents heated to 65°C. After less than an hour, medical staff can simply read the result with the naked eye. This is in contrast to the current nasal test method that requires several hours of laboratory processing and extensive equipment and reagents, and with results often not delivered for days.
France is already a European leader in terms of saliva testing. A revolutionary test called EasyCov was developed in less than three months by the Sys2Diag laboratory in Montpellier.
This test is similar in ways to a pregnancy test. The color of a saliva-soaked tablet will indicate whether or not virus antibodies are present without any need to go to a laboratory for analysis.
“To develop and mass produce a test in just three months, it is not enough to invent something in a lab, you have to quickly combine the clinical and industrial aspects. When you have all three together, you go fast and you get it done," said project leader and biologist Franck Molina to the French National Center for Scientific Research.
The principle underlying this saliva PCR test is the same as for the classic nasal PCR, but the process is much faster and easier. “PCR tests are seen as the gold standard, the most reliable one at the moment,” confirms Luke O’Neill, professor of immunology at Trinity College Dublin, speaking with FRANCE 24. “The dose of the virus in your body determines your level of infectiousness. The lower the dose you have, the less likely it is you will infect other people.”
Low number of false positives
The first clinical trials for this new EasyCov test were carried out between April and May on 133 patients at Montpellier University Hospital. The results showed a high sensitivity to detecting the virus and a very low number of false positives. Intermediate results will be announced at the end of September and submitted to a scientific review committee.
There are also two main supporting clinical trials to understand the role saliva plays in the progress of the virus.
The ‘Covisal’ trial started at the end of July in French Guiana. Its objective is to validate that using saliva is as effective as nasal swabs. In concrete terms, the study aims to collect mucus and saliva from symptomatic people arriving at the emergency room of Cayenne University Hospital who are suspected of having Covid-19, to create a kind of saliva reference library.
"We hope to know by the end of September whether it is possible to switch to saliva sampling and under what conditions," virologist Bruno Lina, a member of the scientific council, told Le Monde.
A second-stage study called ‘Salicov’ is due to start testing soon at the Assistance publique-Hôpitaux de Paris (APHP). Its aim is to assess the value of saliva samples for screening purposes. Two samples – nasal and salivary – will be taken at the same time.
Pharmacy blood test already available
France already has blood tests available without prescription in pharmacies, which check for coronavirus antibodies. These rapid tests cost from around €15 and you get the results in 15 minutes.
The tests are known as “TROD” in French - meaning “tests rapides d’orientation diagnostiques” or “rapid diagnostic guidance tests”. There are 51 such tests currently authorized by the ministry of health.
The blood test uses a few drops of blood from a pinprick on your finger and is administered by a pharmacist, who will then interpret your results.
These tests also identify the presence of antibodies, which suggest you have been infected with the virus within the past two to three weeks.
O’Neill adds that it is important to remember that no test can offer an "immunity passport”.
“We are still a long way from knowing how immune you might be if you have already contracted the virus. We are still finding out how long the antibodies can live within people – and there are vastly differing results. But there is no proof that if you have caught the virus once that you will not catch it again.”
“But we need to find a way to live with the virus now, we can’t just pause our lives until a vaccine arrives. This is like living in the middle of a hurricane, we need to build shelters,” says O’Neill. “Testing is extremely important, though it is still largely a work in progress. We are learning so much about this virus so fast.”