Impact of physical distancing measures against COVID-19 on contacts and mixing patterns: repeated cross-sectional surveys, the Netherlands, 2016–17, April 2020 and June 2020

  1. Jantien A Backer
  2. Liesbeth Mollema
  3. Eric RA Vos
  4. Don Klinkenberg
  5. Fiona RM van der Klis
  6. Hester E de Melker
  7. Susan van den Hof
  8. Jacco Wallinga

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Abstract

During the COVID-19 pandemic, many countries have implemented physical distancing measures to reduce transmission of SARS-CoV-2.

Aim

To measure the actual reduction of contacts when physical distancing measures are implemented.

Methods

A cross-sectional survey was carried out in the Netherlands in 2016–17, in which participants reported the number and age of their contacts the previous day. The survey was repeated among a subsample of the participants in April 2020, after strict physical distancing measures were implemented, and in an extended sample in June 2020, after some measures were relaxed.

Results

The average number of community contacts per day was reduced from 14.9 (interquartile range (IQR): 4–20) in the 2016–17 survey to 3.5 (IQR: 0–4) after strict physical distancing measures were implemented, and rebounded to 8.8 (IQR: 1–10) after some measures were relaxed. All age groups restricted their community contacts to at most 5, on average, after strict physical distancing measures were implemented. In children, the number of community contacts reverted to baseline levels after measures were eased, while individuals aged 70 years and older had less than half their baseline levels.

Conclusion

Strict physical distancing measures greatly reduced overall contact numbers, which likely contributed to curbing the first wave of the COVID-19 epidemic in the Netherlands. However, age groups reacted differently when measures were relaxed, with children reverting to normal contact numbers and elderly individuals maintaining restricted contact numbers. These findings offer guidance for age-targeted measures in future waves of the pandemic.

Article activity feed

  1. Version published to 10.2807/1560-7917.es.2021.26.8.2000994
  2. Version published to 10.1101/2020.05.18.20101501v2 on medRxiv
  3. ScreenIT

    SciScore for 10.1101/2020.05.18.20101501: (What is this?)

    Please note, not all rigor criteria are appropriate for all manuscripts.

    Table 1: Rigor

    Institutional Review Board Statementnot detected.
    RandomizationParticipants were randomly selected from the Dutch population registry using a two-stage cluster design.
    Blindingnot detected.
    Power Analysisnot detected.
    Sex as a biological variablenot detected.

    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:
    To assess the representativeness of the survey participants, a few potential limitations need to be addressed. First, not all of those who were invited to the survey, participated, causing a potential for selection bias. Second, there are differences in participant characteristics between the surveys, for instance participant age, sex, household size and contact day. We determined the weighted average number of contacts to account for these differences (see S1.3), and found that only the participant age altered the unweighted averages by about 10%. This does not affect the results as they are all stratified by age. Third, the 2020 surveys were carried out in time windows of one month (April and June), whereas the baseline survey was conducted over a period of almost two years. Because contact patterns change little throughout the course of a year (see S1.4 and [16]), we do not expect this to substantially affect the estimated reduction. Finally, the surveys consisted of different but overlapping study populations. To check whether this had any effects on the results, we repeated the analysis on 1,739 participants that were common to all surveys. This longitudinal study showed that – although baseline levels were a bit higher – trends and reductions were similar to the main analysis (see S1.5). During strict physical distancing, the number of community contacts was drastically reduced in all age groups. When these measures were relaxed, elderly persons largely kept their conta...

    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.

    About SciScore

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  4. Version published to 10.1101/2020.05.18.20101501v1 on medRxiv