Estimating the effect of mobility on SARS-CoV-2 transmission during the first and second wave of the COVID-19 epidemic, Switzerland, March to December 2020

  1. Adrian Lison
  2. Joel Persson
  3. Nicolas Banholzer
  4. Stefan Feuerriegel

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Abstract

Human mobility was considerably reduced during the COVID-19 pandemic. To support disease surveillance, it is important to understand the effect of mobility on transmission.

Aim

We compared the role of mobility during the first and second COVID-19 wave in Switzerland by studying the link between daily travel distances and the effective reproduction number ( R t ) of SARS-CoV-2.

Methods

We used aggregated mobile phone data from a representative panel survey of the Swiss population to measure human mobility. We estimated the effects of reductions in daily travel distance on R t via a regression model. We compared mobility effects between the first (2 March–7 April 2020) and second wave (1 October–10 December 2020).

Results

Daily travel distances decreased by 73% in the first and by 44% in the second wave (relative to February 2020). For a 1% reduction in average daily travel distance, R t was estimated to decline by 0.73% (95% credible interval (CrI): 0.34–1.03) in the first wave and by 1.04% (95% CrI: 0.66–1.42) in the second wave. The estimated mobility effects were similar in both waves for all modes of transport, travel purposes and sociodemographic subgroups but differed for movement radius.

Conclusion

Mobility was associated with SARS-CoV-2 R t during the first two epidemic waves in Switzerland. The relative effect of mobility was similar in both waves, but smaller mobility reductions in the second wave corresponded to smaller overall reductions in R t . Mobility data from mobile phones have a continued potential to support real-time surveillance of COVID-19.

Article activity feed

  1. Version published to 10.2807/1560-7917.es.2022.27.10.2100374
  2. ScreenIT

    SciScore for 10.1101/2021.04.16.21255636: (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: We did not detect open data. We also did not detect open code. Researchers are encouraged to share open data when possible (see Nature blog).

    Results from LimitationRecognizer: We detected the following sentences addressing limitations in the study:
    This study is subject to several limitations. First, our analysis was limited to Switzerland. While the overall course of the epidemic in Switzerland is characterized by a similar variability seen in many European countries, a future comparison with other countries could be especially valuable to investigate country-specific differences in mobility behaviour. Second, we used mobility data only from a sample of the population in Switzerland, which was however selected to be representative by age, gender, and region. Third, in our study, mobility was measured via the daily travel distance. Other studies have analysed mobility in the first wave using alternative metrics such as the radius of gyration or trip counts,[2] which may have different interpretations. However, as our model measures changes in mobility on a relative scale, we expect our results not to be highly sensitive to the choice of metric. In our models, both the mobility variables and the time-varying effective reproduction number Rt were smoothed with a 3-day moving average. Our estimates are therefore with respect to smoothed mobility and Rt. We further acknowledge that the estimation of Rt can entail considerable uncertainty, especially when the number of reported cases is low. We addressed this limitation by selecting only study periods with a substantial proportion of infectious persons and thus comparatively small uncertainty. To capture structural changes in transmission aside from mobility, we fitted separ...

    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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  3. Version published to 10.1101/2021.04.16.21255636v1 on medRxiv