Covid-19: Three big questions we’re now asking

This week’s rogue case of Covid-19 has prompted a flurry of questions about New Zealand’s exposure to the coronavirus. Science reporter Jamie Morton looks at three of them.

Is it time to turn down the travel tap?

More than 100 cases of Covid-19 have been detected at the border already this month – roughly the same number as recorded across the months of November and December respectively.

This afternoon, the Ministry of Health told the Herald 12 positive cases had been confirmed among guests at Auckland’s Pullman Hotel alone, between the infected Northland woman arriving there on December 30 and yesterday.

With rampant case rates around the world, and the emergence of faster-spreading variants, the threat at our borders has never been greater.

Yet, even after 100,000 returnees coming home since March last year, and strict entry requirements largely making only permanent residents and citizens eligible to come here, the country’s managed isolation and quarantine (MIQ) facilities are still running close to capacity.

Importantly, Otago University epidemiologist Dr Amanda Kvalsvig noted MIQ guests are arriving from countries that have very high infection rates, with increasing numbers of highly infectious variants.

“Guests and staff in MIQ now have a high risk of becoming infected and that also creates risk for the whole country, as we’ve just seen with the current Northland case,” she said.

“It’s not in people’s best interests to travel all this way, only to become ill on arrival in New Zealand and perhaps infect others too.”

She said a temporary reduction in MIQ numbers was one of an array of actions that could be taken to give the system a chance to adjust to the increase in risk.

“For example, slightly lower occupancy would make it easier to work on ventilation in MIQ hotel rooms and bring them up to a safer standard.”

Experts have also suggested tightening travel restrictions for people coming from mass-infected countries.

Prime Minister Jacinda Ardern said no country had barred their citizens from returning, as this would essentially leave them stateless.

She added the Government had rolled out N95 masks more widely, required pre-departure testing before flying here and introduced new protocols around people leaving MIQ rooms before their first test results came in.

“We are constantly looking at what we can do to create further restrictions and protocols to protect people, both in our facilities but also in our wider population,” she said.

“But you would be hard pressed to find anyone with more stringent measures than we have at our border.”

Are MIQ air vents a hidden risk?

The possibility that the virus could have been passed from one isolating returnee in Auckland’s Pullman Hotel to another through ventilation systems is a curious one.

As Health Minister Chris Hipkins said this afternoon, it was also the least likely, with surface contamination or close contact the more probable explanation.

Still, do air ducts in managed isolation and quarantine (MIQ) facilities pose an overlooked Covid-19 threat?

The fact that 100,000 people have now passed through MIQ facilities, with comparatively few travellers catching the virus in them, would suggest that risk is low.

Otago University infectious diseases expert Professor David Murdoch explained the virus was passed on through droplets – and the smaller aerosols could be suspended in the air and possibly pass through ventilation systems.

“There are lots of questions from researchers around this at the moment.”

There’s been some research to suggest the same ventilation systems found in many modern office buildings, which are designed to keep temperatures comfortable and increase energy efficiency, may increase the risk of exposure.

Ventilation, whether driven by wind or heat generated within the building or by mechanical systems, works in one of two main modes.

Mixing ventilation is the most common, where vents are placed to keep the air in a space well mixed so that temperature and contaminant concentrations are kept uniform throughout the space.

The second mode, displacement ventilation, has vents placed at the bottom and the top of a room, creating a cooler lower zone and a warmer upper zone, and warm air is extracted through the top part of the room.

As our exhaled breath was also warm, most of it accumulates in the upper zone.

Provided the interface between the zones was high enough, contaminated air could be extracted by the ventilation system rather than breathed in by someone else.

One study has suggested that, when designed properly, displacement ventilation could reduce the risk of mixing and cross-contamination of breath, thereby mitigating the risk of exposure.

But, like Hipkins, Murdoch said this potential risk needed to be put in the context of the myriad other ways the virus could spread – like through lift buttons and rubbish bins, as seen in New Zealand already.

Will the vaccine be effective against the new variants?

The Government today announced that border and MIQ staff, and their close contacts, would be vaccinated within weeks – and the rest of the country could expect a wider roll-out midway through the year.

Medsafe will be seeking advice and recommendations from the Medicines Assessment Advisory Committee (MAAC) next Tuesday about the Pfizer and BioNTech vaccine.

Would that vaccine, and the other Janssen, Novavax, and University of Oxford-AstraZeneca vaccines New Zealand has pre-purchased, work just as well against the emerging UK, South African and Brazil variants?

“There are thousands of variants now out there, but with most of them there is no difference to the way that your immunity recognises them,” University of Auckland vaccinologist Associate Professor Helen Petousis-Harris explained.

“But if the shape of the target that you’ve made an immune response against changes significantly, that could make it less effective.”

Pfizer-BioNTech has stated its vaccine was still effective against the UK and South Africa variants – although it was slightly less protective against the latter.

“Unlike for influenza vaccines, the reduction in neutraliaation that might indicate the need for a strain change has not been established for Covid-19 vaccines,” said a study that tested the Pfizer-BioNTech vaccine on the variants.

AstraZeneca was currently testing its vaccine against them.

Petousis-Harris said it was critical to consider the difference between vaccine efficacy – or how it performed under ideal and controlled circumstances – and “effectiveness”, or its performance in real-world conditions.

“Effectiveness can be ultimately much higher than efficacy, because of its additional effects on transmission,” she said.

“So you could have a very average vaccine that could potentially get rid of a disease, just because of the more indirect effects that you see once you start using it.”

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