Non-pharmaceutical interventions (NPIs) to cut COVID-19 mortality, care demand

NeilMFerguson, Daniel Laydon, Gemma Nedjati-Gilani,Natsuko Imai, Kylie Ainslie, Marc Baguelin, Sangeeta Bhatia, Adhiratha Boonyasiri, Zulma Cucunubá,Gina Cuomo-Dannenburg,Amy Dighe, Ilaria Dorigatti, Han Fu, Katy Gaythorpe, Will Green, Arran Hamlet, Wes Hinsley,Lucy C Okell, Sabine van Elsland, Hayley Thompson, Robert Verity, Erik Volz, Haowei Wang, Yuanrong Wang, Patrick GT Walker, PeterWinskill, CharlesWhittaker, ChristlADonnelly, Steven Riley, AzraCGhani.On behalf of the Imperial College COVID-19 Response TeamWHO Collaborating Centre for Infectious Disease ModellingMRC Centre for Global Infectious Disease AnalysisAbdul Latif Jameel Institute for Disease and Emergency AnalyticsImperial College LondonCorrespondence: neil.ferguson@imperial.ac.uk
Summary
The global impact of COVID-19 has been profound, and the public health threat it represents is the most seriousseen in a respiratory virus since the 1918 H1N1 influenza pandemic.Here we present the results of epidemiological modelling which has informed policymaking in the UK and other countries in recent weeks. In the absence of a COVID-19 vaccine, weassess thepotential role of a number of public health measures –so-called non-pharmaceutical interventions (NPIs) –aimed at reducing contactrates in the population and thereby reducing transmission of the virus. In the results presented here, we apply a previously published microsimulation model to two countries: the UK (Great Britain specifically) and the US. We conclude that the effectiveness of any one intervention in isolationis likely to be limited, requiring multiple interventions to be combined to have a substantial impact on transmission. Two fundamental strategies are possible: (a) mitigation, which focuses on slowing but not necessarily stopping epidemic spread –reducing peak healthcare demand while protecting those most at risk of severe disease from infection, and (b) suppression, which aims to reverse epidemic growth, reducingcase numbers to low levels and maintaining that situation indefinitely.Each policy has major challenges. We find that that optimal mitigation policies (combining home isolation of suspect cases, home quarantine of those living in the same household as suspect cases, and social distancing of the elderly and others at most risk of severe disease) might reduce peak healthcare demand by 2/3 and deaths by half. However,the resulting mitigated epidemic would still likely result inhundreds of thousands of deaths and health systems (most notably intensive care units) being overwhelmed many times over.For countries able to achieve it, this leaves suppression as the preferred policy option. We show thatin the UK and US context, suppression will minimally requirea combination of social distancing of the entire population, home isolation of casesandhousehold quarantine of their familymembers. This may need to be supplemented byschool and university closures, though it should be recognised that such closures may have negative impacts on health systems due to increased

absenteeism. The major challenge of suppression is that this type ofintensiveintervention package –or something equivalently effective at reducing transmission –will needto be maintained until a vaccine becomes available (potentially 18 months or more) –given thatwe predict thattransmission will quickly rebound if interventions are relaxed.We show that intermittent social distancing –triggered by trends in disease surveillance –may allow interventions to be relaxed temporarily in relative short time windows, but measures will need to be reintroduced if or when case numbersrebound.Last, whileexperience in Chinaand now South Korea showthat suppression is possible in the shortterm, it remains to be seen whether it is possible long-term, and whether the social and economic costs of the interventions adopted thus far can be reduced.