Rapid antigen tests are part of the tool kit for the Government’s Covid-19 response, with a phased controlled rollout. Epidemiologist Michael Baker explains why this will deliver better health outcomes.
In October it was announced that rapid antigen tests, often abbreviated ‘RAT’ would be trialled in 29 workplaces, following a rollout in Auckland’s Middlemore Hospital.
The trials helped form a wider rollout of rapid antigen testing to other groups and settings as part of the Government's ongoing response to Covid-19, leading to an announcement on Thursday that RATs will be used in other settings from next month.
Associate Minister of Health Dr Ayesha Verrall announced the new national testing strategy, in line with the introduction of the new traffic light system which begins at 11.59 on Thursday December 2.
The strategy is hoped to provide greater protection for high-risk groups, Verrall said.
“Our testing strategy has worked well to date. New Zealand has amongst the highest number of tests per positive case in the OECD and our border testing has stopped potential incursions.
“When we were pursuing an elimination strategy we relied on highly sensitive PCR tests because the cost of missing a case was too high.
“With more and more New Zealanders gaining protection through vaccinations, we can now introduce a wider range of routine testing options that provide other benefits such as accessibility, convenience and speed.
“With more Covid-19 cases appearing around the country, testing, tracing and quickly isolating cases and their contacts will be all the more important for protecting whānau and communities," Verrall said.
“We will focus surveillance testing and contact tracing where it’s most needed, to find and minimise Covid-19."
Nasopharyngeal PCR tests will continue to be used as the primary diagnostic test, but this will be supplemented by saliva-based PCR testing, rapid antigen testing and rapid PCR tests.
“From 1 December, businesses will be able to directly source from authorised suppliers approved rapid antigen tests for use within their workforce. These tests will be more widely used across the health system, including aged residential care.
“Rapid antigen tests will also be available to the general public at pharmacies from 15 December, with tests to be administered under the supervision of pharmacy staff. A PCR test will be required to confirm any positive results,” Verrall said.
Under the new framework, in regions at Red and Orange there will be a focus on symptomatic testing and surveillance testing in high-risk settings.
Regions at Green will see a greater focus on surveillance testing, to quickly find any new clusters of cases.
A move to test more quickly
Rapid antigen tests offer a quicker result (about 15 minutes) than the commonly used PCR tests - which involve a nasal swab and are processed in a laboratory, usually within 24-48 hours.
They are also less invasive than PCR tests, with a swab around the bottom of each nostril, rather than reaching up to the back of the nasopharyngeal area.
Australia introduced rapid antigen tests for sale in supermarkets, petrol stations and convenience stores this month. Health Minister Greg Hunt emphasised the less-accurate tests were not a replacement for standard PCR tests.
"It's an additional support and an additional screening tool rather than a pure diagnostic tool," Hunt told reporters.
And while there has been a lag in RATs being introduced as a readily available testing option in New Zealand, the Ministry of Health says part of the reason for this, is rapid antigen tests lack the technology to link it to an individual’s My Covid Record.
My Covid Record was rolled out this month, and gives individual’s a platform to access vaccination records, apply for a vaccine passport and certificate and have the most recent positive or negative Covid test results recorded.
The Covid-19 test results link is not yet active on the platform but is "coming soon" according to the ministry.
“There are also technology considerations, including the need to develop agreements with vendors to connect with the national laboratory database for processing and recording of test results,” a Ministry of Health spokesperson told 1News.
Baker in favour of a phased rollout
Epidemiologist, professor Michael Baker says he supports the Ministry of Health's position in regards to a measured rollout.
“At the elimination stage it was important to be able to detect every single case in every single setting so we could stop cases from transmitting any further. So we needed the most sensitive possible test. That’s when you really are hunting for a needle in a haystack," Baker says.
“If you were flying into MIQ we wanted to detect all the positive cases there, so a PCR test was a better diagnostic tool.
“As soon as we move from elimination to suppression, we are trying to minimise transmission, so we are more tolerant of missing the occasional case so we can accept less sensitive testing that has other advantages like low cost, speed and convenience.
“At the moment RATs are done by a designated person, rather than self-testing and that’s the right thing to do because the quality of the sample may not be as good in a self-testing scenario."
There are four reasons why it’s important that RATs are used in a supervised way by someone experienced, Baker says.
“First, if it’s done by a health professional the quality will be better and more consistent.
“Second, if you are found to be positive, you would have a PCR test to confirm it, so there would be a high view of certainty at that point.
“Third, is that you would be given proper advice over self-isolation measures.
“A fourth reason is the recording of an infected person can be added into the national database to provide useful health data on the behaviour of the pandemic,” Baker says.
“It may well be in the future that rapid antigen tests may be more widely used but it’s better to roll them out in a measured and supervised way to achieve the best health outcomes.”
RATs to be used at airports for pre-departure testing
Covid-19 Response Minister Chris Hipkins confirmed on Wednesday that New Zealand would be using rapid antigen tests more widely, especially at airports.
"We're going to see situations where rapid antigen testing is more widely used as part of those pre-departure testing requirements and is more likely to be more widely available at airports, or near to airports, for people to satisfy those pre-departure testing requirements.
"That will mean people are being tested much more closely to their departure than potentially 72 hours before they leave."
Director General of Health Dr Ashley Bloomfield said three antigen tests had been approved for import and use in New Zealand but other companies were applying to be used here too.
But he said plenty of tests had been ordered for New Zealanders to use.
"We're looking at the use of those more widely across New Zealand, particularly over the summer period to compliment PCR testing, particularly in some holiday spots, there will be much larger numbers of people there," he said.
There are currently three rapid antigen tests authorised for import and supply.
How are RATs different from PCR tests?
According to the Ministry of Health, the rapid antigen test is different from the RT-PCR (Reverse Transcription Polymerase Chain Reaction) test currently widely used in New Zealand which detects genetic material called RNA.
Samples used for RT-PCR tests are collected with nasopharyngeal swabs, a combination oral and nasal swab (oropharyngeal anterior nares), or saliva.
RATs require a higher quantity of the virus to be present in the sample than other Covid-19 testing methods, the Ministry of Health says.
"As a result, RATs are less sensitive at detecting cases, especially in asymptomatic people or people who are early in their infectious period. A positive result in any RAT requires a confirmation test by RT-PCR swab undertaken by a healthcare professional."
"The advantage of RATs is that they give a result quickly, which assists with rapid risk assessment and reduces the amount of time a positive individual is active in the community. RATs can be conducted in a laboratory, a health setting, or in the community e.g., at home."