How and when to use antigen tests - Ciara Kelly answers your questions

Ciara Kelly is a "big advocate" of antigen tests, but says it's important to "empower and educate people about their use".
Stephen McNeice
Stephen McNeice

15.14 23 Nov 2021

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How and when to use antigen te...

How and when to use antigen tests - Ciara Kelly answers your questions

Stephen McNeice
Stephen McNeice

15.14 23 Nov 2021

Share this article

With antigen tests now being recommended more widely across society, many people have been wondering how exactly to use the tests.

Dr Tony Holohan just this week warned that people are "clearly" not using antigen tests appropriately.

On today’s Lunchtime Live, Dr Ciara Kelly - host of Newstalk Breakfast and a former GP - took listeners' questions about how (and indeed when) to use the rapid tests.


She explained: “I’ve been a great advocate of antigen tests for a long time… we need to use every tool in our arsenal in the fight against COVID. It has struck me as foolhardy, short-sighted and even paternalistic that we wouldn’t be using them.

“[The tests] aren’t entirely straightforward - that doesn’t mean we shouldn’t use them, it just means we need to empower and educate people about their use.

“I think some people are not getting a PCR when they get a positive antigen… but the HSE needs to know who has COVID, as that way they can help shut down outbreaks and do contact tracing.

“If you get a negative antigen test, but you’re still symptomatic, you cannot rely on that to say you don't have COVID. You’ve got to get a PCR.”

How far should the swab go up the nose?

“I’ve shown people how far to shove the swab up your nose… and it’s much further than you think. It’s at least 2.5cm or about an inch - much further than you’d usually go up your nose.

“A good thing is to hold the swab - but don’t touch the cotton bit - about 2.5cm from the end, so you can close your eyes and keep going until your fingers hit your nostrils. Then you know you’re far enough - otherwise it’s very tempting to go ‘I think I’ve gone far enough’.

“You kind of go up the nostril, then straight back… and if you can at all go back downwards. You’ll feel a burn, and that’s when you know you’re in the right vicinity.”

When is an antigen test effective?

“I would say there are three stages to COVID. First of all there’s the incubation period between contracting it and developing it. The average of that is about five days, but it can be a bit longer.

“The infective period starts two days before your COVID symptoms start… maybe three to five days after you’ve gotten it… and it runs for somewhere between five and nine days. That’s the infectious period an antigen test will hopefully pick up.

“Then there’s actually the period of you having COVID, between when you have symptoms to when you don’t again. A PCR test will pick up most of that period. Some of those periods do overlap… but they’re not the exact same thing.

“PCRs will probably pick up COVID for around a two-week period… an antigen test will probably pick up COVID in you for around a week.”

Should you meet someone who has a cough but has tested negative on antigen?

“Trust the positive test - believe it when it tells you when you have COVID. But don’t rely on the negative test if you have symptoms.

“If you have symptoms and get a negative antigen test, you still need a PCR.

“In the current climate we’re living in, if you have any symptoms whatsoever… just stay home. There are a percentage of PCRs that are false negatives, and Delta is transmissible like you wouldn’t believe.

“In the past two weeks alone, one in 88 of us have been confirmed as getting COVID. It is also massively underreported… so it’s probably one in 40 or 50 of the population have COVID right now. That means wherever you go, there’s going to be a COVID case.

“If you have symptoms, just please bloody well stay home.”

Should I send my symptomatic daughter and her non-symptomatic siblings to school with negative antigen test results?

“You certainly don’t send a sick kid to school with an antigen test, irrespective of what it says.

“Let’s do our bit to help the teachers and staff - if your child is sick, stay home.

“If you have any respiratory symptoms currently, in this current environment… presume they’re COVID. Presume your daughter has COVID, and therefore you and the rest of your family are close contacts. It’s better you stay at home until you get that PCR result.”

Are saliva antigen tests as accurate as nasal tests?

“A lot of people are asking me which are the best tests… I can’t endorse any individual test, because there a variety of them on the market. They’re all different… I can’t say which is the best one, because I don’t know.

“All I can say is any of them licensed to be used here have been approved, and we’re pretty strict about what we approve. They should all be OK.

“I know parents are asking questions about the saliva test, as the swab up the nose is unpleasant as an adult and doubly unpleasant as a kid.

“I have seen studies that have said that saliva tests are on a par and relatively speaking as accurate as the nasal swabs. But the nasal swabs are the ones most of the studies have been done on… I would say if you can use them, do.

“But if you have a situation where you have a small child or somebody that might have additional needs… if all you can do is a saliva test, I would suggest to do your best.”

My nine-year-old had COVID seven weeks ago and is now off school with a runny nose and sore throat. Should I go straight for the PCR test?

“It’s quite unlikely they have COVID. Indeed, if you go to the HSE website to get a PCR, it says if you’ve had COVID in the last nine months don’t come looking for another test, because they’re presuming post-infection will give you immunity for around nine months.

“But there are no sure things. I do know people who have been diagnosed with COVID twice, and have been diagnosed within that nine months.

“I could never say she definitely doesn’t have COVID, so I would recommend to do an antigen and err on the side of caution.”

I’ve had COVID and am apparently immune. Should I still do antigen tests?

“I’ve been vaccinated and had COVID back in wave one… I still do antigen tests.

“My immunity is probably kaput entirely, and I got the Janssen vaccine in May. That means that vaccine immunity has probably waned as well.

“It’s about how long it has been since you’ve had COVID or had your vaccine.”

Main image: File photo. Andreas Prott / Alamy Stock Photo

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