Published in The Conversation.
Authors: Professor Allan Saul, Professor Margaret Hellard AM, Professor Mike Toole AM, Dr Nick Scott and Dr Romesh Abeysuriya, Burnet Institute.
Residents in Sydney, the NSW Central Coast, Blue Mountains and Wollongong today received confirmation their lockdown would be extended to at least 30 July.
NSW records 97 new COVID-19 cases, lockdown extended for two weeks https://t.co/bUAtqdX8RO
– ABC News (@abcnews) July 14, 2021
But our modelling suggests it may take until the end of the year to get case numbers close to zero, unless more stringent measures are introduced.
NSW health authorities increased restrictions on Friday. These limit outdoor gatherings to two people, exercise to within 10km from your home, and shopping to one person from a household each day, with no browsing.
These restrictions are similar to Victoria’s Stage 3 and came on top of existing rules, which began on June 23, to only leave your home for four reasons: work/education, care/compassion, shopping for essential supplies, and exercise.
But additional measures – at least as strong as in Melbourne’s Stage 4 – are needed to get the greater Sydney outbreak under control.
For Melbourne’s second wave, this included closing non-essential retail, restricting movements to 5km from home and within the hours of 8pm to 5am, and mask-wearing outdoors.
COVID case numbers will fall if Victorian Stage 4 measures are applied in greater Sydney, for at least a month.
Our predictions
Our modelling shows that without the initial stay-at-home orders, the results would have been catastrophic (red line).
NSW’s updated level of restrictions (orange line, similar to Victoria’s Stage 3 + masks) would prevent daily case numbers from increasing further. But it’s not enough to eliminate community transmission before the end of the year.
But if Stage 4 restrictions were applied now (blue line), the epidemic curve would decline sharply.
It’s difficult to estimate the time to return case numbers from current levels to a seven-day average of less than five per day, but it’s likely to take at least a month.
So how did we reach these conclusions? We use two complementary modelling approaches to generate information about the measures needed to get case numbers under control.
Simulating people’s decisions
The first model, COVASIM, simulates individual people who reflect the diversity of the population. Individuals are allocated different numbers of daily contacts and can participate in various activities (for example going to school, work, bars/cafes, shopping, playing sport), which affect their risk of transmission.
People respond differently to COVID-19: whether they get tested, how long they wait before being tested, and how compliant they are with quarantine. For infected people, their infectiousness and disease prognoses also depend on their age and vaccine status.
