September 2, 2020
Written by APPRISE researcher and University of Melbourne Professor Jodie McVernon, Director of Epidemiology at the Doherty Institute.
It’s been sweet relief for Victorians to see reported daily COVID-19 cases in double digits as August moves into September, the first time since early July. The Stage 4 restrictions we’re living under were logically expected to drive numbers down, but the last four weeks have felt interminably long. We have two weeks left to go, and the Premier has promised a roadmap showing the way out of lockdown this weekend. What aspects of the data will be most influential for decision making, and what measures are most likely to be eased in a phased transition back to the ‘new normal’?
Clearly, having gone through all this pain, getting case numbers as low as possible is highly desirable. We know that as restrictions are eased, the potential for infections to spread will increase, so the fewer that remain the better. But not all of the cases reported each day arise from community transmission, with many identified in high risk occupational settings like healthcare, or through links to known outbreaks or family members. Some of these new infections will be identified among people in quarantine, who are effectively ‘in captivity’ and therefore unable to spread disease to others. It’s the mystery cases arising without identified links that will be the most important indicator of the risk of a ‘third wave’.
What measures are most likely to keep community transmission down? Workplaces are a logical point of focus for risk reduction. They bring large numbers of people into close proximity, often across long distances, and the journey to work may provide further opportunities for infection to spread. Working from home, where possible, is likely to be with us for some time. Where people need to come together in essential workplaces, risk mitigations must be put in place including physical distancing, enhanced hygiene measures and personal protective equipment (PPE) appropriate to the context. Many of these COVID-safe practices have matured over recent weeks and months in Victoria and nationally, and have become part of the ‘new normal’.
Healthcare settings and aged care have been a focus of particular attention in recent weeks as places where introduced infections are likely, with enhanced potential for ongoing spread. These sectors are rightly gathering the needed evidence to highlight roles, environments and interactions associated with the highest risk of transmission to determine how best to augment existing risk reduction measures. These priority efforts to protect health workers and the vulnerable are further supported by reduced community transmission, that lowers the risk of infections being imported into care environments.
Superspreading events are a key feature of SARS-CoV-2 transmission and essential for its survival. Throughout the pandemic we’ve seen outbreaks associated with people congregating indoors at religious gatherings, nightclubs and social events. From a single source, large numbers of infections can then be seeded throughout households and the wider community. There’s a clear rationale for reducing mixing group sizes in public and private places to curtail infection spread. Our national roadmap allows these numbers to be greater in outdoor settings where the risk of passing on infection is less and to gradually increase over time as sustained low case numbers strengthen confidence in ‘zero community transmission’.
There’s good evidence that reducing indoor mixing groups to 10 or less works, and contact identification and tracing is made easier by this restriction. However, the mental health impacts of the constraints imposed by current Stage 4 orders are substantial, particularly for those who live alone and are not in intimate partnerships (one of few mixing exemptions). Restoring social connections between families and friends must be a priority for this roadmap. We will be asking our community to sustain behavioural change into the longer term, and all of us will need strong support structures in place to deal with the ongoing challenges of living with this virus.
Evidence on the place of school closures remains unclear. Modelling and statistical analyses of the epidemic course in the US and Europe have found links between closing schools and reduced COVID-19 cases. However, it’s difficult to tease out the effect of this measure from other social restrictions often implemented concurrently, or to know whether it’s mixing in schools per se or the requirement for parents to stay home with children that drives this association. The European Centre for Disease Control has found strong evidence for transmission from adults to children in households, but little between children in schools, a finding consistent with studies from New South Wales. In Sweden, where schools have remained open throughout the pandemic, teachers have been no more likely to be infected with SARS-CoV-2 than any other occupational group.
As we move out of a phase of strongly invigilated controls into a more tolerable phase of restrictions, effective community engagement, clear and consistent messaging that explains the rationale for measures and supports to promote co-operation will all be paramount. Until we have a vaccine, behaviour is our only effective strategy to prevent this disease. The place of the social sciences in communicable disease control has never been clearer.