lab vials

One Twitter user said being tested for Covid-19 with a nasal swab felt like “being stabbed in the brain.” Others described the test as leaving a burning sensation.

Saliva testing offers a painless alternative to nasal swabs. Some saliva tests were approved by the Food and Drug Administration as early as mid-April, but the test is yet to become widespread.

Saliva tests simply involve patients spitting into a tube, which is then processed by a machine to determine if the saliva sample contains molecules of Covid-19 to determine if there is an active infection.

The most commonly used sampling method in testing for Covid-19 is nasopharyngeal swabbing — those are the long swabs that are stuck far up your nose. The sample is then evaluated in a polymerase chain reaction machine, which reads whether bits of the virus’ RNA are present.

Samples of saliva are evaluated in the same PCR machine as swabbing tests.

Saliva testing offers several advantages over more commonly used nasal swab testing: Health care workers do not need to expose themselves to potentially infectious people, using less personal protective equipment. In addition, saliva tests can avoid supply chain challenges with equipment like the long swabs used in certain tests, according to Yale University epidemiology researcher Dr. Anne Wyllie.

Testing has been a persistent concern throughout the pandemic. The nasal swab tests for active infection have raised frequent questions about accuracy, with as many as 30 percent of tests returning false positive results. In addition, antibody or serological testing for the presence of antibodies in the blood that should show past infection with Covid-19 have raised frequent questions about accuracy.  

Early tests and at-home kits

Because of its advantages, medical laboratories rushed to develop saliva testing early in the pandemic.

In mid-April, RUCDR Infinite Biologics, a Rutgers University laboratory, received an emergency-use authorization from the FDA for its saliva test. The university’s test was the first commercial saliva test to receive approval from the agency.

Saliva tests have been used by New Jersey state testing sites since April, but no other states have scaled up any similar tests for state-wide use.

In May, RUCDR Infinite Biologics was approved again by the FDA — this time to produce at-home saliva testing kits in partnership with Spectrum Solutions, an information technology company, and Accurate Diagnostic Labs, a New Jersey-based commercial laboratory. ​

The FDA approved another saliva test for at-home use on June 8. Phosphorus, a genomics start-up, sells its kits on its website, as well as through “partnerships between employers and health care providers.”

Several private companies began selling Rutgers’ at-home test online after it was approved: Vault Health sells test kits for $150 online. Vault employees supervise the patient administering the test via video call. Hims and Hers, a telemedicine company, offers a similar service for the same price.

One Reddit user sought out a saliva test after she exhibited telltale Covid-19 symptoms, including a loss of taste and smell. She ordered a test kit from Vault, and she says her insurance will cover the $150 charge once she sends them the information on the test.

An employee from Vault walked her through the test over Zoom, then instructed her on how to sanitize the return package. She says the process took between 10 and 15 minutes, and received her results two days after mailing in her sample. She tested negative, although she questions the results because she was tested several weeks after she first showed symptoms.

Hospitals developing their own tests

On May 11, the FDA released a new policy on testing for Covid-19 during the “public health emergency” — the agency said that laboratories are not required to seek approval for already-approved tests using new sampling methods. In other words, because saliva tests are processed in the same machines as nasal swab tests, the saliva tests no longer need approval from the FDA.

Some hospitals have taken advantage of the relaxed approval process and moved forward with their own saliva tests.

Memorial Sloan Kettering Cancer Center in New York rolled out a new saliva test last week. The hospital has tested only its own employees with the new test so far.

“We wanted a viable option that required no specialized collection device and could be self-collected, which are the main advantages of saliva testing,” Dr. Esther Babady, a clinical microbiologist at MSKCC who helped develop, wrote in an email.

The samples for testing are self-collected by patients with the supervision of a nurse at the hospital. The test only requires a sterile container for collection, which has no supply chain challenges, according to Dr. Babady.

So far, Dr. Babady says reactions have been positive. “From what I’ve heard, staff is much happier providing a saliva sample than having to get swabbed,” she wrote in an email.

Still, other hospitals have chosen not to pursue saliva testing. The Mount Sinai Hospital in New York chose not to develop a saliva test of their own.

The hospital has not developed a saliva test because of concerns over enzymes and proteins in saliva interfering with the PCR machine detecting Covid-19, according to a spokesperson. The spokesperson did not respond to further requests for comment by time of publishing.

How do saliva tests compare to other tests?

Some studies of saliva tests have found that they perform just as well as nasal swabbing, if not better.

One study published in MedRxiv, a website for non-peer-reviewed science papers, on saliva testing found that saliva samples are equally sensitive as nasopharyngeal swab samples: The saliva test detected virus in positive patients at the same rate as the swab tests. Additionally, two healthcare workers who had been exposed to Covid-19 tested positive on a saliva test days before eventually testing positive on a swab test. According to Dr. Wyllie, who led the study at Yale, this suggests that saliva tests may detect asymptomatic cases better than nasopharyngeal swab testing.

“Why just settle for a swab that we know is less than perfect, when we have got some data showing that saliva could be more perfect,” Dr. Wyllie said in an interview.

The study compared nasopharyngeal swab tests and saliva tests for 44 patients in the hospital as well as 98 asymptomatic workers in the Covid-19 ward.

While Wyllie is confident in her team’s data, other studies on saliva tests have demonstrated varying levels of sensitivity relative to nasopharyngeal swabs.

Dr. David Becker, a researcher at genomics company Helix, led a study also published in MedRxiv suggesting that saliva tests are significantly less sensitive than nasopharyngeal swabs. Becker and his team studied subjects in a community setting, meaning outside of a hospital.

Becker says that more information on saliva testing in a community setting is crucial — saliva testing on subjects outside of the hospital may have a different sensitivity than those in hospitals.

“We need more data in order to really expand saliva across the entire community of testing,” Dr. Becker said in an interview. Helix has decided to move away from saliva testing because, according to Dr. Becker, “the data is not sufficient to support moving forward with saliva.”

“We look forward to seeing more data on community based samples,” Dr. Becker wrote in an email.

Dr. Wyllie says that saliva tests have been slow to become widespread because saliva is not often used in the clinic for testing. “When (the pandemic) happened, no one knew anything about SARS-CoV-2, so you had to default to what you already had in place,” Dr. Wyllie said, which, for most laboratories, was nasal swabs.

Ben Glickman

Ben Glickman is a student journalist at Brown University with experience with data analysis, investigative tools and audio storytelling. He is passionate about holding power...