How effective have Victoria’s lockdowns been? Reflections #46

How effective have Victoria’s lockdowns been? The research shows that they’ve meant a reduction of between 9,000 and 37,000 Covid19 cases up to 31 July, so the lockdowns have probably saved between 100 and 500 lives that would have been lost without them. And that’s just so far.

One very useful piece of research that came out this week came from the Burnet Institute in Victoria is an investigation of the counterfactual  – what might have happened if the Level 3 lockdowns and maskwearing hadn’t happened in Victoria?

The researchers estimated the growth rate of the virus without any further actions to require physical distancing:

We estimate that control measures have reduced the reproduction ratio from 1.75 to 1.16 and averted 9,000–37,000 infections between 2 and 30 July. Despite this reduction, there remains significant ongoing growth, with an estimated further 14% reduction in transmission required to control the epidemic.

So what does this mean? The reproduction ratio (usually called R0, or reff) for the virus is how many people each person passes it to. If it is over 1, then the number of cases will grow, as each new case passes it on to 1 or more people. If it is under 1, then the number of cases will eventually drop to zero, as each new case passes it on to less than one new person (of course it is an average!). I blogged about this back in April, at a time when a much more hopeful piece of research from the Doherty Institute was showing all of the Australian states had a reproduction number of less than 1. In the graph above (which is on a logarithmic scale) you can see the slope of the line changing, as the reproduction number drops. Once the line becomes flat, or starts pointing down, that’s when the reproduction number is less than 1.

The important statistic coming from this research is that up until the end of July (so only three weeks) between 9,000 and 37,000 infections were averted because of the distancing measures. Based on Australian mortality statistics (which show a death rate of just over 1% of cases), that’s between 100 to 500 lives that were saved by the actions of Victorians locking down, and then starting to wear masks. We’ll never know who those people are. And there will be more cases avoided, and lives saved, as the gap between the possible number of cases (with no physical distancing) and the actual cases will continue to grow.

But the reproduction rate above 1 calculated in this study was still too high, which is why most of Victoria moved to Level 4 restrictions from 2 August. This graph of the 7 day moving average of cases since mid June is possibly starting to show the curve turning down.

Since case numbers generally reflect infections that happened around a week before (on average) we could hope to see even faster reductions in Victorian case numbers this week.

Links

With the outbreak in Victoria sadly affecting many aged care facilities, this research from the US suggests that staff links are a major cause of outbreaks in aged care:

In this paper, we perform the first large-scale analysis of nursing home connections via shared staff using device-level geolocation data from 30 million smartphones, and find that 7 percent of smartphones appearing in a nursing home also appeared in at least one other facility—even after visitor restrictions were imposed. We construct network measures of nursing home connectedness and estimate that nursing homes have, on average, connections with 15 other facilities. Controlling for demographic and other factors, a home’s staff-network connections and its centrality within the greater network strongly predict COVID-19 cases. Traditional federal regulatory metrics of nursing home quality are unimportant in predicting outbreaks, consistent with recent research. Results suggest that eliminating staff linkages between nursing homes could reduce COVID-19 infections in nursing homes by 44 percent.

It is interesting that traditional metrics of quality don’t seem to change the Covid19 outcome materially. Perhaps because the quality uplift needed for serious infection control for this disease is too big a jump for an aged care facility, or not a requirement for a high quality metric (at least in the US, where the research was done)?

But while the paid pandemic leave recently announced by the prime minister (for Victorians only) will mitigate staff going to work while sick, to some degree, it is less likely to stop the spreading caused by insecure workers working in more than one facility. It is not clear whether staff working in multiple facilities is a major impact in Australia, but it might be worth investigating policy settings to see whether it can be mitigated with some form of income support for staff in this kind of situation.

Life Glimpses

NSW is now suggesting people “should consider wearing a face mask in situations where physical distancing is not possible.” At a zoom chat I was in this week, it seems that the uptake is very variable across Sydney. On the weekend I counted 5% outdoors, in places where people were walking for exercise. But in some parts of Sydney it seems that the rate is well over 50%, possibly correlated with whether there has been a case nearby recently. I wore a mask to a shop for the first time this week (after my local supermarket was a potential source of infection last week) – I’m going to need to set up my routine for having the masks near the door with the shoes and shopping bags.

This follows Victoria which made masks compulsory on 22 July.

Watching the world news this week, from looking at the incidental crowd shots, Australia does seem to be one of the last countries in the world to take the need for masks seriously, which surprises me. In Sri Lanka (20 million people, 11 deaths to date, around 2,700 cases, so more successful containment than Australia, and in theory less risk of transmission), everyone at the election rally I saw was wearing a mask.

Bit of beauty

I’ve been seeing a few local friends on social media doing the Flat Rock Creek walk, which is a lovely little bushwalk in the middle of otherwise suburban Sydney. We tried it this week, and it was lovely as advertised, as you can see.