Saliva testing remains an important tool for those who require regular Covid-19 checks, like border staff or healthcare workers. Photo / Michael Craig

The Kiwi company behind a just-opened laboratory is keen to see saliva-based testing for Covid-19 rolled out further. Where is the technology at and what's holding it back? Jamie Morton explains.

Where are saliva tests used in NZ right now?

Whether it's been in your car or kitchen, most of us now would've felt a nasal swab at the back of our nostrils.

Testing for Covid-19 in New Zealand is still largely done nasopharyngeally – that is, through drawing samples with a swab in that sometimes hard-to-reach spot behind your nose, and above the back of your throat.

While we heard much about saliva-based testing last year – a procedure essentially just requiring people to spit into a container – the arrival of Omicron and cheap, accessible at-home rapid antigen tests (RATs) bumped it out of the limelight.

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But that doesn't mean we shouldn't be using it more, experts say – or that it's not used here in many places still.

Saliva testing remains an important tool for those who require regular Covid-19 checks, like border staff or healthcare workers.

It's also offered in places like hospitals, for people who can't tolerate a nasal swab, or privately for instances like pre-departure tests and surveillance testing.

Examples include the SalivaDirect method developed by Yale University scientists and now used here and around the world, and the University of Illinois' Shield, used by Rako Science.

New Zealand's saliva-testing capacity has now just expanded with Rako opening a new state-of-the-art medical testing lab in Christchurch, enabling the pathology company to turn around test results inside a day – and urgent samples for Auckland and Canterbury within six hours.

Rako's also just set up a new Queenstown-based collection site to cater to the Southland community, international visitors, and the film industry.

An obvious benefit is they're less invasive. Another is that they're highly accurate – and roughly just as much as a PCR test, as one systematic review found last year.

Rako's saliva test – so far the only one to have been diagnostically validated – was found in one recent study to have 99 per cent accuracy.

"There is increasing data and evidence that the right saliva protocol is more accurate than nasopharyngeal swab test due to the changing morphology of the disease with new variants," Rako executive director Leon Grice said.

But the big strength of Rako's test was that it could pick up an infection before the onset of infectiousness – and still with high accuracy.

"This is a significant advantage over RATs where sensitivity is very low in early infection," he said.

"RAT accuracy tends to coincide with the onset of symptoms, four to five days after infection which means the person will test negative for two to three days when they are viral shedding and spreading the disease."

And how about the cons?

University of Auckland senior lecturer Dr Nikki Freed said the only potential disadvantage to using saliva was that labs doing the testing needed to slightly change the way they processed the samples, show that they are doing the tests correctly, and get approval for it.

"However, these are standard regulatory issues labs deal with when they offer a new test."

For the average Kiwi seeking one, another drawback was time and cost.

Rako's Test2BSure PCR saliva test cost around $115 a pop and, while results are typically delivered within a day, it still required lab processing.

By comparison, a five-pack of RAT tests cost about $30 at the supermarket and delivered quick – albeit sometimes inaccurate – results from home.

For that reason, the Ministry of Health told the Herald that RATs were still New Zealand's "primary testing tool", although a new strategy for the post-peak period was soon to be released.

What about saliva RAT tests?

Saliva-based tests that are just as quick as RATs are indeed out there.

But just not in New Zealand yet, as the 17 ministry-approved products here are all nasal swab tests.

Promising new saliva-based products include the PASPORT test developed by researchers at Singapore's Duke-NUS Medical School, which may be 97 per cent accurate, able to be carried out within 15 minutes at home and similarly priced to RATs here.

"I think RATs that use saliva should absolutely also be offered," Freed said.

"I think saliva is easier for people to self-administer than a nasal swab which can in turn result in more accurate testing.

"RATs that use saliva have been shown to have similar sensitivity and accuracy to nasal swab RATs, which is to say, they are better than nothing, and are great at-home, easy, inexpensive testing."

Should New Zealand be doing more saliva testing?

Kiwi-born Yale scientist Dr Anne Wyllie, who pioneered coronavirus saliva testing with SalivaDirect, certainly saw a greater role for the approach here.

"It can be very quick and easy to give samples, it does not require the presence of a trained healthcare worker, freeing valuable staff," she said.

"Instruction can also be simple: drool into a simple tube, perhaps assisted by a straw or funnel, with the advice not to eat or drink half an hour before - or just have a glass of water 10 minutes before."

That could make testing much more affordable - and even more competitive as compared to antigen tests, if a generic, accessible protocol was used.

Wyllie said saliva-based RATs were particularly exciting, as they could potentially capture people earlier in the infection so stop people spreading the virus for days before nasal swab-based tests turned positive.

She remained frustrated that Omicron had been able to spread through our schools, where simple saliva-based testing programmes could have helped.

"This really could have been mitigated with more robust school or workplace testing - as a number of companies around New Zealand have taken onto themselves to try to protect their staff - and therefore the communities of their staff as well."

NZ Institute of Medical Laboratory Science president Terry Taylor said that, with pressure on lab workers enough to have forced 5 per cent out the door over recent months, his sector welcomed private players like Rako helping to lighten the load.

"We should have had every tool in the toolbox going."

Otago University epidemiologist Professor Michael Baker pointed to another one: loop-mediated isothermal amplification (Lamp) tests.

These were also self-administered like a nasal swab RAT, but offered much more accurate results – and much faster, with results within 30 minutes.

They're now being trialled at Auckland Airport, initially limited to 30 Air NZ staff, and could eventually be used in hospitals, aged care and other sectors.

But Baker said, as with many saliva tests, cost could also be a barrier.

"Because we now have an increasing range of testing options, and some of them are expensive, I think there's a risk of perpetuating a socio-economic gradient."