Impact of non-pharmaceutical interventions (NPIs) to reduce COVID-19 mortality and healthcare demand
Neil M Ferguson, Daniel Laydon, Gemma Nedjati-Gilani, Natsuko Imai, Kylie Ainslie, Marc Baguelin,Sangeeta Bhatia, Adhiratha Boonyasiri, Zulma Cucunubá, Gina Cuomo-Dannenburg, Amy Dighe, IlariaDorigatti, Han Fu, Katy Gaythorpe, Will Green, Arran Hamlet, Wes Hinsley, Lucy C Okell, Sabine vanElsland, Hayley Thompson, Robert Verity, Erik Volz, Haowei Wang, Yuanrong Wang, Patrick GT Walker,Caroline Walters, Peter Winskill, Charles Whittaker, Christl A Donnelly, Steven Riley, Azra C Ghani.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 London
Correspondence:
[email protected]
Summary
The global impact of COVID-19 has been profound, and the public health threat it represents is themost serious seen in a respiratory virus since the 1918 H1N1 influenza pandemic. Here we present theresults of epidemiological modelling which has informed policymaking in the UK and other countriesin recent weeks. In the absence of a COVID-19 vaccine, we assess the potential role of a number ofpublic health measures – so-called non-pharmaceutical interventions (NPIs) – aimed at reducingcontact rates in the population and thereby reducing transmission of the virus. In the results presentedhere, we apply a previously published microsimulation model to two countries: the UK (Great Britainspecifically) and the US. We conclude that the effectiveness of any one intervention in isolation is likelyto be limited, requiring multiple interventions to be combined to have a substantial impact ontransmission.Two fundamental strategies are possible: (a) mitigation, which focuses on slowing but not necessarilystopping epidemic spread – reducing peak healthcare demand while protecting those most at risk ofsevere 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 majorchallenges. 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 theelderly and others at most risk of severe disease) might reduce peak healthcare demand by 2/3 anddeaths by half. However, the resulting mitigated epidemic would still likely result in hundreds ofthousands of deaths and health systems (most notably intensive care units) being overwhelmed manytimes over. For countries able to achieve it, this leaves suppression as the preferred policy option.We show that in the UK and US context, suppression will minimally require a combination of socialdistancing of the entire population, home isolation of cases and household quarantine of their familymembers. This may need to be supplemented by school and university closures, though it should berecognised that such closures may have negative impacts on health systems due to increased absenteeism. The major challenge of suppression is that this type of intensive intervention package – or something equivalently effective at reducing transmission –will need to be maintained until avaccine becomes available (potentially 18 months or more) – given that we predict that transmissionwill 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 inrelative short time windows, but measures will need to be reintroduced if or when case numbersrebound. Last, while experience in China and now South Korea show that suppression is possible inthe short term, it remains to be seen whether it is possible long-term, and whether the social andeconomic costs of the interventions adopted thus far can be reduced.