Ban on antigen Covid testing must end

Dr Eric Crampton
31 August, 2021

As Auckland struggles, hopefully successfully, to bring the current Delta outbreak under control, let us imagine a future variant – the Iota variant. This hypothetical variant is identical to Delta, except for one detail. When someone becomes infectious with it, a prominent rash in the shape of the letter I, for Iota, appears on their forehead.

Obviously, stopping the Iota variant would be much simpler than stopping the Delta variant. And it also gives us just a few obvious hints about better ways of dealing with Delta.

Waking up in the morning, we could each look in the mirror to see whether we had become infectious overnight. If we did, we would have to decide whether to inform the authorities and proceed to an isolation facility, or to stay at home for the duration and infect everyone else in the household.

If we became infectious while heading out for essentials, someone would see the distinctive I on our forehead and tell us to hasten to the nearest isolation facility.

And if we worked in essential services, our foreheads would be checked as we arrived on-shift at the hospital, care facility, or other essential business. We would not put our coworkers at risk, and they would not put us at risk.

The Iota variant would be a walk in the park as compared to the Delta variant. Even if the virus was identical to Delta in every other way, it would struggle to achieve an R0 of even 1 because everyone would know to steer clear.

The Iota variant would struggle to gain any traction at all.

Anything we can do to turn Delta into Iota seems like a good idea.

So how can we shift from Delta to something more like Iota? Better regular testing.

Over a year ago, the University of Toronto’s Professor Josh Gans published The Pandemic Information Gap: The Brutal Economics of Covid-19. He explained how the pandemic is really an information problem. If we all knew who was infected and who was not, pandemic management would be far simpler.

He followed it up in January 2021 with The Pandemic Information Solution: Overcoming the Brutal Economics of Covid-19. As he put it, “Solve the pandemic information problem, save the world.”

We should be applying some of his lessons.

Gans’s first lesson is that tests must be fit for purpose.

If we want to know whether someone we suspect has the virus really does have the virus, PCR tests are most effective. Using them in Managed Isolation, and for close contacts of known cases, makes perfect sense.

But swab-based PCR tests are very expensive, slow to provide results, and invasive. Nobody would want to have one every day, and even if they did, it is not a solution that can possibly scale up.

Saliva-based PCR tests are both cheaper and faster, while remaining highly accurate. They can scale up more reliably than swab-based PCR tests. Gans explains how the University of Illinois tested staff and students twice a week using the testing protocol it developed. By the end of 2020, that single university had conducted over one million tests, with results typically available to students within eight hours. And it has prevented outbreaks.

Antigen tests are not as sensitive as PCR tests overall but are reliable when a person is infectious. For high viral loads, the Abbott BinaxNOW test proved as accurate as PCR tests in one assessment but missed one person whose low viral load was only caught by PCR. The test costs about $5 (more in the United States) and gives results in about fifteen minutes. Other antigen tests are broadly available in Europe, at less than a dollar per test. The Canadian government has been distributing packs of tests to small businesses for employee testing, for free.

These kinds of tests make more sense for broad population screening. If there is no reason to suspect someone has the virus, but you want to prevent infectious people from boarding an airplane, a rapid and low-cost test that can be administered in the departure lounge before boarding makes a lot of sense.

The New Zealand government’s testing regime is almost exclusively swab-based PCR tests. The system very obviously cannot keep up with the amount of testing required in major outbreaks. It takes too long to collect samples; samples must be collected by a limited number of trained professionals; it takes too long to process tests; it takes too long to return results to those who have been tested; and, it is rather expensive.

The University of Illinois’s saliva-based PCR test has been available in New Zealand on a private basis since January, thanks to the University’s New Zealand partner, Rako Science. Rako has advertised that it can test up to ten thousand people per day. Its collection method does not require scarce nurses for sample collection and can be scaled up much more readily. Depending how long it takes to get samples to the lab, it can provide results in about four hours. The Ministry of Health, for months, inexplicably refused to consider adding this option to the government’s testing regime.

But the real testing job is an order of magnitude larger still, if we want to turn Delta into Iota.

The Ministry of Health has reported transmission among essential workers in Auckland. This type of transmission has made it difficult for New South Wales to control its outbreak.

The government could, today, order a couple million rapid antigen tests. They are broadly available. It could distribute those test kits to every essential workplace in Auckland and require that every essential worker be tested every day before starting work.

It could be a condition of a Level 4 modified to suit Delta.

Within about fifteen minutes, each worker’s result would be available. Infectious workers could be sent to government testing stations for confirmation. And workplace transmission would be sharply reduced.

Why are employers not doing this on their own as part of normal health and safety prudence? The tests are currently prohibited in New Zealand. In April 2020, the government banned all point-of-care tests unless they are approved by MedSafe, and MedSafe has not seen fit to approve any tests. Pedants might argue that this does not constitute a ban, but banning anything that has not been approved while deciding not to approve any options sounds an awful lot like a ban. It is unclear whether MedSafe has even evaluated any options.

The most plausible justification for the ban is that the government feared people would fail to report positive results, or would take undue comfort in early negative results before viral load increased, and contribute to outbreaks.

Whatever the merits of the ban prior to Delta, it makes little sense in the context of a Delta outbreak with transmission among essential workers. Providing rapid antigen tests to essential employers, such as hospitals, care homes, and supermarkets, would provide an additional layer of protection. If the government did not want to purchase the tests for those employers, it could at least ease the ban on them.

Antigen tests at essential workplaces would help turn infectious Delta cases into Iota cases. They would prevent a lot of further infection and misery, and would help reduce the duration of lockdown.

The government’s ban on point-of-case testing must end.

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