Large-scale lockdowns and other non-pharmaceutical interventions in Europe have been successful in reducing the transmission levels of SARS-CoV-2.

This is the conclusion of a modelling study from Imperial College London scientists, published online in Nature today, which suggests lockdown measures have been sufficient to control the growth of the epidemic.

This data suggests that without any interventions, such as lockdown and school closures, there could have been many more deaths from COVID-19 Dr Samir Bhatt Study author

The team, from the MRC Centre for Global Infectious Disease Analysis, Jameel Institute (J-IDEA), and Imperial's Department of Mathematics, estimated reductions in transmission based on combined data from 11 European countries up to early May 2020. They caution that the results offer 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 effectiveness

Measuring the effectiveness of these interventions is important, given their economic and social impacts, and may indicate which courses of action are needed in future 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.

Our model suggests that the measures put in place in these countries in March 2020 were successful in controlling the epidemic Dr Seth Flaxman Study author

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  - and the method used by the researchers in this study - 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.

The Imperial team used death data to infer changes in the course of the COVID-19 epidemic as a result of non-pharmaceutical interventions. They analysed data from 11 countries in Europe, including the United Kingdom, Spain, Italy, Germany and Belgium, up until 4 May 2020.

The team estimate that by that date between 12 and 15 million individuals in these countries had 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.

Lockdown prevented deaths

Dr Samir Bhatt, study author from the MRC Centre for Global Infectious Disease Analysis, Jameel Institute (J-IDEA), Imperial College London: “This data suggests that without any interventions, such as lockdown and school closures, there could have been many more deaths from COVID-19. The rate of transmission has declined from high levels to ones under control in all European countries we study. Our analysis also suggests far more infections in these European countries than previously estimated. Careful consideration should now be given to the continued measures that are needed to keep SARS-CoV-2 transmission under control.”

The use of pooled data and the short time separation between subsequent non-pharmaceutical interventions makes it difficult to determine the effect of individual sanctions on the suppression of the COVID-19 epidemic. One limitation of the model is that it assumes that each measure had the same effect on all countries, whereas in reality, there was variation in how lockdown was implemented in different countries. However, the authors conclude that lockdown has a substantial effect in reducing the reproductive number below one and has helped to contain the spread of COVID-19 as of the beginning of May.

Dr Seth Flaxman, study author from the Department of Mathematics, Imperial College London: ”Using a model based on data from the number of deaths in 11 European countries, it is clear to us that non-pharmaceutical interventions– such as lockdown and school closures, have saved about 3.1 million lives in these countries. Our model suggests that the measures put in place in these countries in March 2020 were successful in controlling the epidemic by driving down the reproduction number and significantly reducing the number of people who would have been infected by the virus SARS-CoV-2.”

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‘Estimating the effects of non-pharmaceutical interventions on COVID-19 in Europe’ is published in the journal Nature

Adapted from a Nature press release