More people may be getting a false negative result from rapid antigen tests (RATs) because of how Omicron infects different parts of the body.
Many New Zealanders have said they've tested negative via a RAT, even though they're showing symptoms of COVID-19.
Microbiologist Siouxsie Wiles says RATs need a certain amount of virus for people to test positive. Some people will have symptoms but because they've been vaccinated, it means there isn't enough virus for the test to pick up.
"We actually know that because Omicron infects a slightly different part of the body - so more like the throat than the nose - that some people will never test negative with a nasal swab, actually it needs a throat swab," Wiles told The Project on Thursday.
But that doesn't mean RATs should be swabbed at the back of the throat since they're validated as a nasal swab.
"I think people need to be a little careful. You can certainly try but I wouldn't want anybody hurting themselves by gouging a bit too far," Wiles says.
"Actually one of the other reasons why people can test negative is if they aren't actually swabbing the right part of their nose. So the really important thing to remember is to go low rather than high.
"For these tests, you don't have to go very far, just a couple of centimetres in."
If you have symptoms and return a negative RAT result, that doesn't necessarily mean you don't have COVID - and Wiles recommends you test again.
"If you're someone who's been vaccinated, especially if you've been boosted, you may well have symptoms earlier and so you don't quite have enough virus there," she says.
"But as I say, some people will just never test positive because they don't have much of the virus in their nose, it's much more in their throat."
And a negative RAT doesn't mean you're not contagious if you're someone who has more of the virus in your throat, Wiles adds.
It's one possibility that we're getting more false negatives because New Zealand is a highly-vaccinated country.
"We know that lots of people test negative. Over social media in the last couple of months, there's been lots of people saying they had negative tests with their nasal swabs but as soon as they looked at their throat or saliva they were positive," Wiles says.
"I think this is something that's happening everywhere."
Watch the full interview above.
