Covid: antigen tests, should you test both in the nose and throat?

Published by Laurent P. · Published on 7 January 2022 at 16h17
Faced with Covid Omicron variant – making antigen tests less reliable – should we test both in the nose and throat to get reliable results? Here is more on the matter!

Here is a question tormenting many French… As the Covid Omicron variant is now dominant in the country, but less easily detectable via antigen tests available in pharmacies or self-tests in supermarkets (until January 31), should we test both in the nose and throat as some scientists recommend to make sure results are reliable?

The answer is yes, according to Pr. Jennifer L. Rohn, cell biologist in London: “after a string of negative LFTs, I finally took Twitter advice and swabbed my throat as well as my nose (no mean feat with that diddly stick)”, she explained in a tweet. She adds results are then positive: “If you think you might have COVID, consider adding the throat sample”.

Same call for Doctor Swapneil Parikh – searcher and specialist in internal medicine – as he stated: “Important tip on rapid antigen tests (RAT) for Omicron. In the last 2 days a few of my patients have tested RAT negative when collecting only nasal samples but positive on throat + nasal samples”.

A double swab especially useful in cases of Omicron contamination… And for good reason, “the Omicron variant first emerges in the throat and then only in the nose”, Belgian virologist Marc Van Ranst explained to our Flemish peers on VTM Nieuws. He goes on: “If you test in the nose at the beginning of the disease’s process, the virus is not there yet. But when you add a throat swab, you are more likely to test positive”.

A saliva test is then more effective to find this strain… According to a study released in pre-print this past December 24 on medRxiv, it seems to be the case: it consisted in observing different people who caught different strains of the virus and have them take several saliva and nose tests. And results were crystal clear: nasal PCR tests are 100% effective in detecting the virus including the Delta strain, and 71% when it comes to Omicron.

As for saliva tests, results are switched: “for the Omicron variant saliva and mid-turbinate swabs had a 100% [positive percent agreement]”, the study explains, against 86% for saliva tests in finding the Delta strain. A double swab is then a way to guarantee an Omicron contamination. But the study still has to be peer-reviewed.

Practical information