Omicron variant: Which test is better? Nasal or salivary test?
Omicron has quickly become the dominant Coronavirus variant in the world. It’s more than 50 mutations are responsible for being two to three times more infectious than Delta variants. The higher infectivity of this variant is mainly due to the fact that Omicron attacks and multiplies in the bronchi up to 70 times faster than the Delta variant.
On the other hand, in the lungs, Omicron multiplies 10 times less than the original variant, which contributes to the fact that Omicron has a lower ability to cause a severe course of COVID-19.
The researchers estimate that this difference in multiplication also results in a different incidence of viral load in the saliva, which raises the question: Is sampling of the nasopharynx still the best option?
Does Omicron mean the end of the pandemic?
Initial information suggested that Omicron is a milder variant. We could therefore think that the pandemic is over and the situation in the hospitals will only improve over time.
However, this is unlikely to happen with Omicron’s arrival. Although the Omicron variant has a slightly lower ability to cause a severe course of COVID-19, as it is two to three times more infectious, it affects more people. This also increases the likelihood that more people will have a more severe course of the disease than other options.
Therefore, it is still important to adhere to pandemic measures and the 3 W’s (Wear mask / Watch your distance / Wash hands) principle. In addition, the best prevention is vaccination, and if you have been in contact with someone who is positive or you are experiencing symptoms, do not hesitate to book a test.
In the following lines, we will look at which type of test is the most appropriate according to the latest scientific knowledge.
Saliva or nasal test?
At the beginning of the pandemic, there was a demand for effective testing on COVID-19 due to the identification and isolation of Covid-positive people. At that time, experts determined that the best way to take a sample is from the nasopharynx and the throat. Later, during testing, we also started to meet with shorter test sticks, which were used to take a sample of the nasal area.
However, with the arrival of each new variant, the most appropriate sampling method needs to be reconsidered. While nasopharyngeal or nasal swabs have generally been preferred in previous variants, recent studies and reports from practitioners suggest that with Omicron, this may be different.
Study from South Africa
Fresh Manuscript Study from South Africa suggests that salivary PCR tests may be more reliable than nasal PCR tests because Omicron has a higher viral load in saliva than in the nose compared to the Delta variant.
The researchers examined the positivity of nasal samples against saliva samples. In the Delta variant, saliva samples were worse compared to nasal swabs with only 71% positivity. In contrast, the Omicron variant had a more reliable saliva sample. The nasal swab had 86% positivity compared to the saliva sample.
“Nasal swabs have been the standard for COVID-19 screening and diagnosis since the virus was discovered, but this may no longer be the case in an environment where Omicron is dominant,” the study authors concluded.
Study from the USA
Another manuscript from the US suggests that nasal antigen tests cannot detect a patient infected with omicron at the time of its greatest infectivity. The study found that the salivary viral load peaked in some patients during the first to second days – before nasal antigen tests showed a positive result.
“Both nasal antigen (AG) and PCR tests are able to detect an infectious patient 1 to 3 days later than salivary AG or PCR tests can. The study also found out that a nasal PCR test reveals a positive test usually one day before a nasal AG test,” explains epidemiologist Michael Mina, MD, PhD.
These studies support previous reports in which experts and tested patients have described that they passed a positive saliva test on the same day or before a negative nasal test.
However, the professionals do not unanimously agree on the introduction of saliva tests as a testing standard. While one group calls for an immediate change in the testing standard for COVID-19, others recommend waiting for more robust data and taking action if the findings so far are confirmed.
What do these findings mean?
In an environment with a dominant Omicron variant, it is not possible to rely on a negative result of the nasal, especially antigenic, test. Recent scientific evidence suggests that a nasal test (whether AG or PCR) may not detect COVID-19 infection at the onset of the disease when you are already highly infectious.
Therefore, if you want to be tested, the salivary PCR test will be the most suitable option for the Omicron variant. This type of test is currently only offered by private laboratories.