Stopping future waves of COVID-19 might require coordinated lockdowns across the globe, rather than letting each country do its own thing, epidemiologists say.
The pandemic started in China, but quickly made its way across the world - first devastating Europe before the epicentre moved to New York and the US, followed by a surge in South America. Presently India is recording the majority of new cases.
New Zealand is believed to have eliminated community transmission of the virus earlier this year after implementing one of the world's toughest lockdowns, enjoying a brief return to near-total freedom between June and August. But with the pandemic still raging elsewhere it came back, just a week after Director-General of Health Ashley Bloomfield said a resurgence was "inevitable".
A new paper published in journal Proceedings of the National Academy of Sciences says with each country doing something different, at different times, in the absence of a vaccine the virus will continue to thrive.
"The intensity and implementation time of these actions varied considerably across countries in the initial wave, which may explain much of the variation in infection rates that exists between populations and countries.
"However, a pandemic is defined by its global spread, and the effectiveness of coordinating global suppression efforts in subsequent waves of the pandemic has not yet been fully projected."
The scientists at Tsinghua University simulated the virus' spread and found simultaneously locking down 15 major world cities had the potential to cut new case numbers by almost 90 percent.
"Concerns are growing over the negative impacts of sustained social lockdowns and travel restrictions on economies, so it is important to explore control approaches that are both rapid and effective."
The primary "hubs", as they were dubbed, are: New York, Philadelphia, Los Angeles, Washington DC, London, Paris, Shanghai, Shenzhen, Hong Kong, Zurich, Mumbai, New Delhi, Jerusalem, Tokyo and Singapore.
An "intensive" eight-week lockdown which reduces travel - and transmission - by 80 percent, combined with as-needed lockdowns in 44 secondary locations (including Sydney, Stockholm, Moscow and Wuhan), would reduce new cases about 88 percent, achieving "control of transmission" in more than three-quarters of them.
Other scenarios - such as longer, but less restrictive lockdowns - weren't nearly as successful, according to the modelling. Locking down all 59 cities at once for eight weeks would only have a "marginal" improvement over the hub/secondary split plan, but would be far more economically damaging and much more difficult to coordinate.
"Practically, we suggest a tiered implementation of this strategy where interventions are first implemented at locations in what we call the Global Intervention Hub (GIH), followed by timely interventions in secondary high-risk locations," the study reads.
"We argue that thinking globally, categorising locations in a hub-and-spoke intervention network, and acting locally, applying interventions at high-risk areas, is a functional strategy to avert the tremendous burden that would otherwise be placed on public health and society."
Even if the secondary cities didn't take part, locking down the 15 hubs would reduce the caseload by about 42 percent, the scientists said.
"The extent to which we can successfully mitigate the next waves of the pandemic is strongly dependent on how all nations collaborate. Importantly, the disease burden of COVID-19 could be significantly reduced through the initial intervention, as coordinated by the GIH in the early stages. This intervention effect would be consolidated by timely and intensive actions among remaining high-risk locations."
Modelling has formed a big part of New Zealand's strategy at wiping out COVID-19, with the Government taking a largely risk-averse approach when it comes to moving down alert levels, on the advice of scientists.
The confirmed COVID-19 death toll passed the 1 million mark this week, but the true toll is likely to be much higher, the World Health Organization says, with many deaths likely going unreported as being due to COVID-19.
