Large-scale lockdowns and other non-pharmaceutical interventions in Europe have been successful in reducing the transmission levels of SARS-CoV-2 enough to control the epidemic growth, suggests a modelling study. The estimated reductions in transmission are based on combined data from 11 European countries up to early May 2020, offering a general view of the current situation that may not fully account for differences in approaches.
From 2–29 March 2020, European countries began implementing major non-pharmaceutical methods (such as school closures and national lockdowns) to control the COVID-19 epidemic. Measuring the effectiveness of these interventions is important, given their economic and social impacts, and may indicate which course of action is needed to maintain control. Estimating the reproduction number – the average number of cases an infected person is likely to cause while they are infectious – is a useful measure. However, the reproduction number can be difficult to calculate using case data, as a larger proportion of infections are likely to go unreported. An alternative way to track an epidemic is to calculate infection levels retrospectively by analysing reported deaths. Although death data may also be subject to under- or misreporting, it is considered more reliable than case data, and can also be useful to estimate the share of unreported cases.
Seth Flaxman and colleagues at the MRC Centre for Global Infectious Disease Analysis, Jameel Institute for Disease and Emergency Analytics, Imperial College London, use death data to infer changes in the course of the COVID-19 epidemic as a result of non-pharmaceutical interventions. They analyse data from 11 countries in Europe, including the UK, Spain, Italy, Germany and Belgium, up until 4 May 2020. They estimate that by that date between 12m and 15m individuals in these countries have been infected with SARS-CoV-2 (3.2% to 4% of the population, with large country-to-country fluctuations). By comparing the number of observed deaths against those predicted by their model in the absence of interventions, the authors suggest that approximately 3.1 million deaths have been averted due to non-pharmaceutical measures. They calculate that the reproduction number has dropped to below one as a result of the interventions, decreasing by an average of 82%, although the values vary from country to country.
Abstract
Following the emergence of a novel coronavirus1 (SARS-CoV-2) and its spread outside of China, Europe has experienced large epidemics. In response, many European countries have implemented unprecedented non-pharmaceutical interventions such as closure of schools and national lockdowns. We study the impact of major interventions across 11 European countries for the period from the start of COVID-19 until the 4th of May 2020 when lockdowns started to be lifted. Our model calculates backwards from observed deaths to estimate transmission that occurred several weeks prior, allowing for the time lag between infection and death. We use partial pooling of information between countries with both individual and shared effects on the reproduction number. Pooling allows more information to be used, helps overcome data idiosyncrasies, and enables more timely estimates. Our model relies on fixed estimates of some epidemiological parameters such as the infection fatality rate, does not include importation or subnational variation and assumes that changes in the reproduction number are an immediate response to interventions rather than gradual changes in behavior. Amidst the ongoing pandemic, we rely on death data that is incomplete, with systematic biases in reporting, and subject to future consolidation. We estimate that, for all the countries we consider, current interventions have been sufficient to drive the reproduction number RtRt below 1 (probability RtRt< 1.0 is 99.9%) and achieve epidemic control. We estimate that, across all 11 countries, between 12 and 15 million individuals have been infected with SARS-CoV-2 up to 4th May, representing between 3.2% and 4.0% of the population. Our results show that major non-pharmaceutical interventions and lockdown in particular have had a large effect on reducing transmission. Continued intervention should be considered to keep transmission of SARS-CoV-2 under control.
Authors
Seth Flaxman, Swapnil Mishra, Axel Gandy, H Juliette T Unwin, Thomas A Mellan, Helen Coupland, Charles Whittaker, Harrison Zhu, Tresnia Berah, Jeffrey W Eaton, Mélodie Monod, Imperial College COVID-19 Response Team, Azra C Ghani, Christl A Donnelly, Steven M Riley, Michaela AC Vollmer, Neil M Ferguson, Lucy C Okell, Samir Bhatt
[link url="https://www.nature.com/articles/s41586-020-2405-7"]Nature abstract[/link]