The Australian Government is moving in the right direction. The Prime Minister announced this morning a ban on non-essential indoor gatherings of 100 people or more, in addition to the ban on outdoor gatherings of 500 or more. The travel ban has been extended to all countries. Visits to aged care facilities are restricted. The importance of spatial isolation has been reiterated.

But results from these sensible measures won’t be evident immediately. In fact, as the Figure below shows, the coronavirus continues to grow rapidly in Australia. We are still on the ‘scary’ part of the curve. As of yesterday, we had 449 confirmed COVID-19 cases. Italy had about the same number of cases on February 26, and now has more than 28,000.

We don’t know how the number of Australian cases will grow in the future. Spain, Iran, and Italy stayed roughly on the path of doubling every two days (shown above). France and the UK doubled every 3 days. Singapore has managed to slow its growth, with cases now doubling every 10 days. In the past week, Australia has doubled its cases every 3-to-4 days.

The actual number of people infected with COVID-19 is likely to be larger than we know now. It takes time for somebody to contract the virus, develop symptoms, get a test, and then get diagnosed. The Figure below shows the number of new cases each day in China between January and early February. The researchers, Wu and McGoogan, used detailed patient records to establish when symptoms first became apparent (in red) and when people were diagnosed (in orange).

Chinese cities were put into lockdown from 24 February. By then, the ‘real’ rate of new infections was five times higher than newly diagnosed cases. The lockdowns slowed the growth in people reporting symptoms almost immediately, but official numbers continued to grow for 7-to-10 days.

The impact of the new measures Australia has introduced will take time to show up in official cases. It’s a step in the right direction, but we are unlikely to see the flow-through to lower case numbers for another week.

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