And what if saliva tests were more likely to detect the Covid Omicron variant? This is what searchers who released a pre-print study on MedRxiv this past December 24th, say, adding saliva PCR tests were far more effective, even 100% in cases of detection the Omicron variant. A study that also brings a few more details about the effectiveness of nasal PCR tests, enabling to detect this new stress less easily, but that yet remain useful in the fight against the spread of the epidemic.
What does the study read exactly? First, it involved 382 patients, all carrying different strains of the disease, and asymptomatic. Between August and December 2021, each one of them has been tested with different process (nasal PCR, throat swabs…). Tests that have been then sequenced to find out which variant searchers were dealing with (Delta or Omicron). And results are really clear!
Scientists have reported nasal PCR tests were much more effective, 100%, to detect the Delta variant, but only 71% to detect the Omicron variant. As for throat PCR tests, it is the other way around: they are more effective to detect the Omicron variant, at 100%, than detecting the Delta variant (at 86%).
The effectiveness of the saliva tests can be explained by the fact the incubation time is shorter. When nasal testing, the virus might have not developed in the nose yet as epidemiologist Michael Mina explains on Twitter: “This means that there is a chance the virus isn’t yet growing in the nose when you first test. Virus may start further down. Throat swab + nasal may improve chances a swab picks up virus”.
Symptoms are starting v early w Omicron (for a number of reasons I’ve discussed)— Michael Mina (@michaelmina_lab) December 27, 2021
This means that there is a chance the virus isnt yet growing in the nose when you first test
Virus may start further down. Throat swab + nasal may improve chances a swab picks up virus. https://t.co/NfxHqjKpIo
Another reason of this effectiveness? The fact this strain of the virus, in all likelihood, first grows in the throat: “The Omicron variant is first detected in the throat and only later in the nose”, Belgian virologist Marc Van Ranst told our peers from VTM Nieuws. He went on: “If you collect nasal swabs at the beginning of the disease, the virus might not be there yet. But when you combine it with a throat swab, you have more chances to test positive”. Hence the interest of double swab.