Perfect timing for flu mitigation measures
Close schools, cancel major events, restrict non-essential travel? When a severe strain of flu is on the rampage, public distancing methods rank prominently among the possibilities health authorities may consider to limit transmission. There will often be calls to apply such measures sooner rather than later. But new EU-funded research shows there are situations where it may actually pay to wait. The study, funded in part by the SARSTRANS ('Control policy optimisation for severe acute respiratory syndrome (SARS) and other emerging infections: characterising transmission dynamics and estimating key epidemiological parameters') project, is presented in the journal PLoS Computational Biology. SARSTRANS received EUR 1.7 under the 'Life sciences, genomics and biotechnology for health' thematic area of the EU's Sixth Framework Programme (FP6). Researchers at Imperial College London in the UK and Utrecht University in the Netherlands used mathematical models to analyse the impact of short-term interventions on the transmission of influenza and the effectiveness of flu reduction policies. Key parameters for their analysis notably included a hypothetical six-month lead time for the availability of a strain-specific vaccine. They also considered various scenarios for the availability of pre-pandemic vaccines at the beginning of the outbreak. The team found that distancing measures introduced a few weeks into the epidemic are nearly as effective as immediate implementation when it comes to reducing the extent of an epidemic and limiting the peak number of cases. In fact, given that such measures cannot be maintained indefinitely, their timing must be considered carefully for maximum effectiveness. 'If you can only use an intervention for a limited period of time, then it's likely that there will be a resurgence of the epidemic after the intervention is lifted,' says Dr Deirdre Hollingsworth, a Junior Research Fellow from the Medical Research Council Centre for Outbreak Analysis and Modelling at Imperial College London, one of the co-authors of the study. 'This happened in a number of American cities after the 1918 pandemic. Waiting a few weeks before starting to implement containment policies can reduce this resurgence,' she adds. 'If it is not possible to eradicate an epidemic, it is often assumed that you need to deploy all of your mitigation options as soon as possible,' Dr Hollingsworth explains. 'But we found that waiting a few weeks is as effective at achieving key public health aims as starting interventions immediately. If you take into account the impact that those policies will have on society, it might be better to hold back at the start.' Professor Sir Roy Anderson of Imperial College London, a senior author on the study, notes that 'Simple models of epidemics can exhibit complex behaviours and it is important to understand these dynamic patterns when designing optimal control policies. This is especially the case for influenza A epidemics that move on a fast time scale of weeks and months as opposed to years.' The study suggests that the best timing for intervention will depend on the precise policy objectives public health authorities decide to pursue. In addition to limiting mortality, there may, for example, be constraints linked to the availability and ongoing supply of treatments, or the peak number of cases public health services could handle. Optimising policies for one of these objectives may limit the scope to achieve others. 'National plans for dealing with pandemics set out various policy options,' says Dr Hollingsworth, 'but there is rarely any clear statement of their objectives. Different objectives can conflict with each other, so it's vital to set out your priorities.'For more information, please visit: Imperial College London: http://www3.imperial.ac.uk/ Utrecht University: http://www.uu.nl/EN/Pages/default.aspx SARSTRANS project factsheet on CORDIS, click: here PLoS Computational Biology: http://www.ploscompbiol.org/doi/pcbi.1001076
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Netherlands, United Kingdom