Optimising social mixing strategies to mitigate the impact of COVID-19 in six European countries: a mathematical modelling study
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Abstract
Background
If SARS-CoV-2 elimination is not feasible, strategies are needed to minimise the impact of COVID-19 in the medium-to-long term, until safe and effective vaccines can be used at the population-level.
Methods
Using a mathematical model, we identified contact mitigation strategies that minimised COVID-19-related deaths or years of life lost (YLLs) over a time-horizon of 15 months, using an intervention lasting six or 12 months, in Belgium, France, Italy, Spain, Sweden and the UK. We used strategies that either altered age- or location-specific contact patterns. The optimisation was performed under the constraint that herd immunity should be achieved by the end of the intervention period if post-infection immunity was persistent. We then tested the effect of waning immunity on the strategies.
Findings
Strategies of contact mitigation by age were much more effective than those based on mitigation by location. Extremely stringent contact reductions for individuals aged over 50 were required in most countries to minimise deaths or YLLs. The median final proportion of the population ever-infected with SARS-CoV-2 after herd immunity was reached ranged between 30% and 43%, depending on the country and intervention duration. Compared to an unmitigated scenario, optimised age-specific mitigation was predicted to avert over 1 million deaths across the six countries. The optimised scenarios assuming persistent immunity resulted in comparable hospital occupancies to that experienced during the March-April European wave. However, if immunity was shortlived, high burdens were expected without permanent contact mitigation.
Interpretation
Our analysis suggests that age-selective mitigation strategies can reduce the mortality impacts of COVID-19 dramatically even when significant transmission occurs. The stringency of the required restrictions in some groups raises concerns about the practicality of these strategies. If post-infection immunity was short-lived, solutions based on a mitigation period designed to increase population immunity should be accompanied with ongoing contact mitigation to prevent large epidemic resurgence.
Article activity feed
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SciScore for 10.1101/2020.08.25.20182162: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Our approach has some technical limitations. We used previously published synthetic contact matrices, which allowed a consistent approach across the six countries and incorporation of location-specific contact rates35. The model assumes that mixing patterns in countries are well represented by these matrices and does not capture repeated contacts between the same individuals. We chose to mitigate the age-specific contact rates by applying a …
SciScore for 10.1101/2020.08.25.20182162: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Our approach has some technical limitations. We used previously published synthetic contact matrices, which allowed a consistent approach across the six countries and incorporation of location-specific contact rates35. The model assumes that mixing patterns in countries are well represented by these matrices and does not capture repeated contacts between the same individuals. We chose to mitigate the age-specific contact rates by applying a single multiplier to each age-group, whereas more flexibility could be introduced by allowing mixing between particular pairs of age-groups. Given the important uncertainties in the current epidemiological knowledge of SARS-CoV-2, we chose broad ranges of parameter values to inform the most critical aspects of the model, which translated into moderate uncertainty ranges for several epidemiological indicators. However, we believe our approach to handling uncertainty is appropriate to the current stage of the pandemic. Finally, the optimised strategies identified in this study may become suboptimal if the background epidemiological conditions changed significantly. In particular, we anticipate that as the epidemics progress, population immunity will naturally increase such that reduced levels of transmission may be required during the optimised phase to achieve herd immunity. However, the fact that we observed very similar optimal mixing patterns across the six countries, whereas the level of population immunity at the start of the mitigatio...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
Results from rtransparent:- Thank you for including a conflict of interest statement. Authors are encouraged to include this statement when submitting to a journal.
- Thank you for including a funding statement. Authors are encouraged to include this statement when submitting to a journal.
- No protocol registration statement was detected.
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SciScore for 10.1101/2020.08.25.20182162: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
Our approach has some technical limitations. We used previously published synthetic contact matrices, which allowed a consistent approach across the six countries and incorporation of location-specific contact rates35. The model assumes that mixing patterns in countries are well represented by these matrices and does not capture repeated contacts between the same individuals. We chose to mitigate the age-specific contact rates by applying a …
SciScore for 10.1101/2020.08.25.20182162: (What is this?)
Please note, not all rigor criteria are appropriate for all manuscripts.
Table 1: Rigor
NIH rigor criteria are not applicable to paper type.Table 2: Resources
No key resources detected.
Results from OddPub: Thank you for sharing your code.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
Our approach has some technical limitations. We used previously published synthetic contact matrices, which allowed a consistent approach across the six countries and incorporation of location-specific contact rates35. The model assumes that mixing patterns in countries are well represented by these matrices and does not capture repeated contacts between the same individuals. We chose to mitigate the age-specific contact rates by applying a single multiplier to each age-group, whereas more flexibility could be introduced by allowing mixing between particular pairs of age-groups. Given the important uncertainties in the current epidemiological knowledge of SARS-CoV-2, we chose broad ranges of parameter values to inform the most critical aspects of the model, which translated into moderate uncertainty ranges for several epidemiological indicators. However, we believe our approach to handling uncertainty is appropriate to the current stage of the pandemic. Finally, the optimised strategies identified in this study may become suboptimal if the background epidemiological conditions changed significantly. In particular, we anticipate that as the epidemics progress, population immunity will naturally increase such that reduced levels of transmission may be required during the optimised phase to achieve herd immunity. However, the fact that we observed very similar optimal mixing patterns across the six countries, whereas the level of population immunity at the start of the mitigatio...
Results from TrialIdentifier: No clinical trial numbers were referenced.
Results from Barzooka: We did not find any issues relating to the usage of bar graphs.
Results from JetFighter: We did not find any issues relating to colormaps.
About SciScore
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