Coronavirus: 'Optimistic' to assume COVID-19 will contained after 28-day lockdown - study

Relaxing strict lockdown measures will see the coronavirus come storming back, separate studies here and abroad have found. 

New Zealand and China are being held up as examples to follow when it comes to stopping the spread of SARS-CoV-2, the virus which causes COVID-19, responsible for nearly 100,000 deaths worldwide to date. 

China, where the virus began, has managed to almost completely stamp out local transmission (at least according to official figures, which have been eyed with skepticism by some experts); and New Zealand's fast move to pandemic alert level 4 - before we even had a single death - has made headlines around the world.

It's made us one of just a few countries in the world with COVID-19 cases that hasn't experienced an exponential growth in the number of confirmed infections. On Thursday, 15 days into the lockdown, only 29 new cases were reported - a number that appears to be trending downwards.

Kiwi researchers at Te Punaha Matatini on Thursday said New Zealand had a chance at eliminating the virus completely, meaning the only way it could get here would be people bringing it in from overseas - like measles. 

But their mathematical modelling, based on data recorded up until April 5, found it would be "optimistic" to assume a four-week lockdown could achieve that. In "realistic" and "pessimistic" scenarios, an outbreak would still ensue if level 4 restrictions were lifted after 28 days. 

28 days
28 days of lockdown. Photo credit: Te Punaha Matatini

"These scenarios would require the re-imposition of level 4 control at a later stage if this second outbreak were to be controlled," the researchers said. 

Even a 45-day lockdown would contain the virus' spread, but not wipe it out, in an "optimistic" scenario; while a 90-day lockdown would give us the chance of eliminating it completely. 

Te Punaha Matatini 90 days
Ninety days of lockdown. Photo credit: Te Punaha Matatini

"Longer control periods allow for containment in realistic scenarios with rapid case isolation. Longer control periods are more likely to be able to reduce the number of cases so levels where COVID-19 might be eliminated." 

Graph showing the likely outcomes under different lockdown scenarios and assumptions.
Graph showing the likely outcomes under different lockdown scenarios and assumptions. Photo credit: Te Punaha Matatini

The good news is that since Te Punaha Matatini's models were run on April 5, the number of confirmed new cases of COVID-19 has dropped each day. The Government says it won't decide on whether the alert level will drop until two days before the current lockdown is due to end - April 20. Prime Minister Jacinda Ardern has warned everyone should "prepare for alert level 3" just in case.

But like the Te Punaha Matatini study, overseas research has found such a move might be premature. Scientists at the University of Hong Kong looked at how relaxing lockdown measures in China might work.

Lockdowns work by restricting contact between people, cutting off the virus' chances of infecting a new host. This reduces what scientists call its R0 number - how many people the average patient will go on to infect, on average. Above one, and the virus will spread; below one, and it will eventually die out.

The Hong Kong researchers said health authorities will need to keep a close eye on the virus' R0 figure as restrictions are lifted in different regions - while good for the economy, ending lockdowns will increase the likelihood of a "second wave" of infections. 

"While these control measures appear to have reduced the number of infections to very low levels, without herd immunity against COVID-19, cases could easily resurge as businesses, factory operations, and schools gradually resume and increase social mixing, particularly given the increasing risk of imported cases from overseas as COVID-19 continues to spread globally," said Professor Joseph T Wu, who co-led the research, published in The Lancet.

Herd immunity works when the vast majority of people are immune to the disease, preventing it from spreading. This can happen via vaccines - of which none are yet available for COVID-19 - or developing antibodies after being exposed to the virus. As a relatively new disease, it's not clear yet how well our immune systems do this with COVID-19.

"Although control policies such as physical distancing and behavioural change are likely to be maintained for some time, proactively striking a balance between resuming economic activities and keeping the reproductive number below one is likely to be the best strategy until effective vaccines become widely available," said Prof Wu. 

Despite the promising drop in new cases in New Zealand, in an editorial for the New Zealand Medical Journal published on Friday, University of Otago researchers said eliminating COVID-19 from our shores was far from guaranteed. 

If it fails, Kiwis will have to be prepared for "a potential shift to the suppression or the mitigation strategy", where we try to slow the spread of the virus, whilst getting some degree of our old lives back.

"The exit path will need to be based on demonstrable high-performing border controls and case and contact follow-up, along with sufficient testing and surveillance to detect a low risk of COVID-19 circulation in the population. 

"Under these circumstances, the lockdown can be gradually relaxed, potentially on a regional basis."

If elimination fails, they warn more than half of Kiwis could eventually be infected and 14,400 die, based on the disease's current known mortality rate and an R0 of about 2.5. Successful mitigation and suppression could lower both these figures if a vaccine is developed soon enough.