Covid-19

Covid-19: How to avoid the second wave

Analysis: As New Zealand eases restrictions, it no longer has international precedent to look towards and must decide on its own how to reopen the economy while reducing the risk of a second wave of infections, Marc Daalder reports

While most of the country eagerly awaits a likely move to Level 1 by June 10, the thought keeps Michael Baker up at night.

Baker is an expert in infectious diseases at the University of Otago, Wellington's public health department, a member of the Government's technical advisory group for Covid-19 and one of the first individuals to call for New Zealand to lockdown. He's concerned that, as we lift restrictions and as New Zealanders become more complacent with those guidelines still in place, a case of Covid-19 that sneaks into the country could blossom into a cluster which would put us right back into Level 2 or worse.

"These are exactly the questions that give epidemiologists sleepless nights. The first sleepless nights were really three months ago when the virus was upon us. You know, the enemy was at the gates. We just had to act so quickly and we had no alternative, I think, to what we did," Baker told Newsroom.

"Now, it's different. There's all the cliches about how coming down from the mountain was tougher than climbing it. But the enemy was at the gate and now - I don't like the war metaphors but - it's guerilla warfare or asymmetric battle. You've got the virus out there but you can't see it. People will naturally get complacent and mistakes will happen."

What will New Zealand's epidemiological controls look like, even as we lift the bulk of the social distancing restrictions, to ensure we really do win this war?

While for months New Zealand has had the advantage of looking to overseas precedent to determine what did and did not work elsewhere in responding to the virus, our successful response now puts us in the position of having to make it up as we go. With a handful of notable exceptions - Taiwan, Mongolia and Vietnam among them - no other country is easing restrictions to the extent New Zealand is.

Whether we want it or not, New Zealand is now going where almost no one has gone before.

Keep it out

Although there is a low risk of any unknown active cases of Covid-19 in the country, the virus is still ravaging nations outside our borders. This puts us in the position, essentially, of returning to the start of our pandemic plan and enacting the first and most important tact: keeping it out.

We have run our response to the coronavirus off the 2017 Influenza Pandemic Plan (IPP). While the plan doesn't call for closing our borders - a factor which led to much criticism of New Zealand's pandemic preparedness in the early months of the crisis - that has since clearly been overturned.

"If the country remains sealed up and has minimal entry, then it's got minimal risk of being exposed," Baker said.

For the time being, the borders will remain shut. Even the much-touted trans-Tasman bubble would only be "realistic" in September, Jacinda Ardern has said. Ardern has not ruled out the possibility of technology changing to allow an earlier opening - for example, rapid and accurate 15-minute Covid-19 tests which would be applied to passengers before boarding aircraft overseas and again after landing. This, however, also seems unlikely to eventuate in the short-term.

Therefore, our borders are largely sealed tight. There are only a few ways in which the virus could reenter the country, all of which have been the focus of Ministry of Health efforts.

To begin with, there is the two weeks of managed isolation or quarantine for returning New Zealanders and those lucky enough to receive an economic or humanitarian exemption to the border closure. While the incubation period for Covid-19 is generally 14 days, there are examples of patients manifesting symptoms more than two weeks after infection. Such an incident here could lead to reintroduction of the virus.

There are also health and hospitality staff operating within the isolation hotels who could be vectors for transmission, although the Ministry of Health has assured the public that these individuals have PPE and protocols in place to reduce this risk. The incident in a Wellington hotel this past week, in which regular guests mingled unknowingly with film workers from the United States who were meant to be in managed isolation, does raise questions about the effectiveness of the isolation regime.

"There's a lot of potential for things to go wrong," Baker said.

As part of the effort to reduce risk from the isolation regime, Director-General of Health Ashley Bloomfield said on Wednesday that he would like to see every person arriving in the country tested twice - first upon entry and then again at some point during their stay in isolation.

International air crews, which are exempted from the isolation regime, could also see a tightening of restrictions. Bloomfield said he was interested in testing some Air New Zealand staff upon reentry and that new protocols were being devised specifically for crews that had travelled to the United States, where one in every 173 people has tested positive for Covid-19.

The other possible transmission vector is cargo ship crews. Although the borders are closed, trade continues via flight and ship. Bloomfield said Wednesday that the Ministry was looking at the protocols around workers on these ships.

Stamp it out

This is all well and good, Baker says, but the country still has to be prepared in the event a case does make it in. To do so, we return to the second phase of the IPP: Stamping it out.

"The stochastic process is all about level of risk and volume of travellers coming into the country. The health protection mantra is you need a multi-barrier approach," Baker said.

"All sorts of things will go wrong and then you just have to say, what are your additional layers of protection?"

For Baker, this involves engaging with the most important figure in basic epidemiology, the reproduction number. The reproduction number, often written as R0, is the number of people the average case will infect. If that number is above one, the number of cases will increase. If it is below one, the number of cases will decrease.

The base R0 for the coronavirus, before taking into account public health measures, is thought to be somewhere around 2.5 or three. That means that without intervention, each infected person will infect 2.5 to three others, who will each infect another 2.5 to three others, and so on.

There are generally three ways to reduce the R0, Baker said. One is by reducing the amount of time someone is infectious, through treatment with antivirals. This option is not yet available, as an effective treatment for Covid-19 has not been identified.

"The duration of infectivity is a biological constant but you can shift it if you have antivirals, which we don't have yet," he said.

The second is reducing the number of physical contacts each person has, on average. That's what the lockdown did and is also the purpose, with lesser effectiveness, of gathering size restrictions and social distancing measures in shops and on public transport.

This method is on its way out the door, as tens of thousands of people will be able to gather in sports stadiums under Level 1 and most indoor social distancing restrictions are expected to be lifted.

"Now, at Level 1, it's pretty much open slather, because we're not limiting contacts," Baker said.

"So only there's one remaining component of the reproduction number you can influence. And that's the probability of transmission between contacts."

This is about coughing into our elbows, washing our hands, staying home when sick and avoiding handshakes. However, given that this is the only method available to us for lowering the R0, Baker wants to see additional measures added.

For him, the obvious choice is masks in close, indoor quarters - particularly public transport.

"The other barrier I've been talking a lot about is masks. We are increasingly one of the only countries that doesn't have a policy on using face masks. All we know about the biology of this virus says we're missing an essential barrier there," he said.

"At the moment, the mantra is stay at home when you're sick, and then wash your hands and cough into your elbow. Well, [the latter two] don't help you much when you're on a crowded bus or in a crowded bar, because it's a respiratory disease. Many of the people who are most infectious don't know it yet, they're not symptomatic. Talking, laughing, singing, we know are very good at transmitting this virus in indoor environments."

Without masks, asymptomatic people could quickly and unknowingly spread the infection.

"Someone who's infectious then goes to a busy event or a bar or a nightclub and they could infect a lot of people very quickly. We just don't have a barrier for that. Hand washing isn't helpful there because people are not necessarily touching surfaces and coughing into your elbow doesn't help you because you're not coughing yet because people don't have symptoms. The only barrier that works is the mask and this is what's being realised across the globe now. And it's not everywhere, but we're really saying we need to have this as a policy for the transport system, for buses, trains and aircraft."

Test, trace, isolate

So, a case sneaks past the border measures. Undetected, the spreading begins, but that spread is slowed and hampered by a prevalence of masks on public transport and good cough etiquette, as well as those who manifest symptoms staying home. Still, in this hypothetical scenario, the virus is out there - how do we stop it before it takes root once more?

To truly stamp out any small outbreak, we need to return to the public health fundamentals that have worked so well overseas: testing, tracing and isolating.

The Ministry of Health can now conduct 12,000 Covid-19 tests a day. Even as we enter flu season and people become more likely to experience symptoms - a cough, a sniffle, a fever - we must continue to robustly test for the virus, Baker says.

For weeks now, the country has effectively tested every sniffle in an effort to root out Covid-19. Now, to ensure it doesn't come back, that widespread testing must continue.

"There are two backstops. One is the testing. The full range of testing of everyone who is symptomatic, some testing of asymptomatic staff at borders and arriving passengers who are asymptomatic as well and this move towards sewage testing," Baker said.

If a positive case is found, everyone that person has been in close contact with will have to be traced and asked to self-isolate for 14 days. Baker wants to see the contact tracing regime set up during the lockdown maintained. While these individuals may not have much work at the moment, they need to be ready to stamp out any potential outbreak before it spreads.

"Obviously having contact tracing working well is the second backstop," he said.

Part of this will involve the deployment of a successful technological solution. The Government's Covid-19 contact tracing app has limited functionality at the moment, but an update to add more features is expected this month. Bloomfield has also said he wants to make it mandatory for businesses to print out and display a compatible QR code, although the Government has not made any announcements to this regard.

However, Baker says the majority of the tracing work will still be done manually.

Easing restrictions while keeping backstops in place to stop the spread of any potential irruption of the virus is no easy work. It will require continued alertness on behalf of health officials monitoring the border and the internal situation.

However, the largest obstacle, Baker says, is complacency on behalf of the general population. If, after months of no new cases, we stop washing our hands as often, stop sneezing into our elbows, skip wearing masks on public transport, venture into work with a sniffle and forget to sign the contact tracing register at the cafe, then we risk aiding the spread of undetected Covid-19.

"The big worry ultimately is complacency," Baker said.

This is what keeps Baker up at night. The systems needed to effectively keep it out and stamp it out are something he, by and large, has confidence in.

On the other hand, the willingness of the New Zealand population to keep working as a team of five million, even when it seems silly or pointless? That's up to each of us.

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