Modelling the impact of the tier system on SARS-CoV-2 transmission in the UK between the first and second national lockdowns
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Abstract
To measure the effects of the tier system on the COVID-19 pandemic in the UK between the first and second national lockdowns, before the emergence of the B.1.1.7 variant of concern.
Design
This is a modelling study combining estimates of real-time reproduction number R t (derived from UK case, death and serological survey data) with publicly available data on regional non-pharmaceutical interventions. We fit a Bayesian hierarchical model with latent factors using these quantities to account for broader national trends in addition to subnational effects from tiers.
Setting
The UK at lower tier local authority (LTLA) level. 310 LTLAs were included in the analysis.
Primary and secondary outcome measures
Reduction in real-time reproduction number R t .
Results
Nationally, transmission increased between July and late September, regional differences notwithstanding. Immediately prior to the introduction of the tier system, R t averaged 1.3 (0.9–1.6) across LTLAs, but declined to an average of 1.1 (0.86–1.42) 2 weeks later. Decline in transmission was not solely attributable to tiers. Tier 1 had negligible effects. Tiers 2 and 3, respectively, reduced transmission by 6% (5%–7%) and 23% (21%–25%). 288 LTLAs (93%) would have begun to suppress their epidemics if every LTLA had gone into tier 3 by the second national lockdown, whereas only 90 (29%) did so in reality.
Conclusions
The relatively small effect sizes found in this analysis demonstrate that interventions at least as stringent as tier 3 are required to suppress transmission, especially considering more transmissible variants, at least until effective vaccination is widespread or much greater population immunity has amassed.
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SciScore for 10.1101/2021.02.23.21252277: (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 and data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Our approach has a number of limitations. While the latent factors account for confounding to some degree, the coefficients we estimate are noncausal and therefore provide only associative effects. We do not consider the interaction of interventions, but merely their joint effect as mandated through the Tier system. In generating counterfactuals our model makes a “difference in differences” counterfactual assumption, which has …
SciScore for 10.1101/2021.02.23.21252277: (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 and data.
Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:Our approach has a number of limitations. While the latent factors account for confounding to some degree, the coefficients we estimate are noncausal and therefore provide only associative effects. We do not consider the interaction of interventions, but merely their joint effect as mandated through the Tier system. In generating counterfactuals our model makes a “difference in differences” counterfactual assumption, which has previously been shown to have limitations [11] arising from the assumption of parallel trajectories. It is important to note that the effect sizes we model quantify the instantaneous and constant impact of the Tiers on Rt, whereas the effects of Tiers may vary over time, perhaps with a lag before they take effect or with a waning of efficacy. Our backdating of Tiers is imperfect: government announcement of a given Tier may have an additional effect beyond that of the particular NPIs within that Tier. However, it remains a reasonable approximation that enables the analysis of NPIs in finer detail than lockdown. It would be useful to measure the effects of the specific interventions that and comprise the Tiers, as this would enable more targeted measures for COVID-19 control. However, the data is unfortunately insufficiently powered to make such inferences. Our analysis focussed on the period between the first and second national lockdowns, before the emergence of the more-transmissible B.1.1.7 variant and before the rollout of vaccination. This focus avo...
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.
- No funding statement was detected.
- No protocol registration statement was detected.
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