Coronavirus: How false-negatives at the border could let COVID-19 back into NZ

"Virtually the whole country is susceptible to COVID-19 infection," Kiwi experts say, thanks to our lack of restrictions at alert level 1 and the high probability some infected people are testing negative in managed isolation (MIQ).

They're calling for pre-flight tests and quarantine in parts of the world where the virus is rampant, new facilities to be constructed outside of city centres and mandatory mask use on public transport, in GP waiting rooms and hospitals at level 1. 

"There are indications that the border system may be experiencing many false negative results in addition to the known positives," an editorial in Friday's edition of the New Zealand Medical Journal (NZMJ) reads.

That's when a person tests negative, but is infected. 

"Because no test is perfect, a negative COVID-19 result does not rule out infection: it only means that the person is less likely to be a case than if they had tested positive."

Genomic testing during the first wave of infections in March showed "only 19 percent of introduced sequences resulted in onward transmission of more than one case", a study published last week in Nature showed. A quarter only infected one other person, while most - 57 percent - didn't infect anyone else at all.

"The converse of this observation is that the number of true introductions of COVID-19 into communities is likely to be larger (and may be much larger) than the number of observed outbreaks," the editorial says.

An analysis earlier this year found possibly one-in-five people with the virus could test as negative, perhaps as many as one-in-three, likely due to problems with sample collection. The Government's MIQ website seems to acknowledge this, saying a negative test on day 12 of a new arrival's stay suggests they have "low risk of having or transmitting COVID-19".

"Even if tested routinely, as in the MIQ system, RT-PCR tests can return a false negative result if the timing of the test is not optimal," the editorial reads.

Michael Baker.
Michael Baker. Photo credit: Newshub.

And as New Zealand has found in the eight known failures at the border, the virus can be tricky -  people don't need to be in the same room at the same time for transmission to occur.

The authors say this is not just a risk to border workers, but their close contacts "with few restrictions when away from border settings, as if their level of risk was the same as the general population".

"The default response setting of alert level 1 includes minimal measures to prevent undetected transmission in public spaces; New Zealanders mix freely in crowded indoor settings and few wear masks unless required to do so. Virtually the whole country is susceptible to COVID-19 infection."

All of New Zealand has been at level 1 since October 7, after the large Auckland outbreak - whose origin remains a mystery - was quashed.

They're calling for an urgent review of the border system.

"High priorities are likely to include switching to a risk-based approach with additional measures, particularly pre-travel quarantine and testing, for travellers from high incidence countries, to prevent them arriving in New Zealand while infected."

Director-General of Health Ashley Bloomfield in October said pre-departure tests weren't needed at this stage because the MIQ system "is working". Epidemiologists, including Michael Baker - one of the authors of this new editorial - have said it would be a good idea.

"The single most important measure for New Zealand is to introduce a way of reducing the number of infected people arriving back into the country," Dr Baker told Newshub Nation in November.

"One approach would be a traffic light system, where we put much more effort into what you could say is the red zone - countries where there is uncontrolled transmission. One option would be to have an additional step before people get on flights from those countries to reduce the risk of them being infected - that could include a brief period of quarantine and a negative test."

The National Party pushed for pre-departure tests during the election campaign, but lost. 

"It just makes sense," deputy leader Shane Reti told Newshub Nation in November. "It seems like it's only the Government that is saying no, and every other expert in the community is saying yes."

A spokesperson for COVID-19 Minister Chris Hipkins said he would be addressing the concerns sometime later on Friday morning.