Social contact patterns in the EU/EEA during the COVID-19 pandemic
This survey (CoMix) was conducted to enhance our understanding of contact mixing during the transition period beyond the acute phase of the COVID-19 pandemic.
In 2020, in response to the COVID-19 pandemic, population-wide non-pharmaceutical interventions were adopted in the European Union/European Economic Area (EU/EEA) with the aim of reducing close-contact transmission between people. This necessitated new data collections of updated contacts. As a result, the European Commission funded the longitudinal contact mixing (‘CoMix’) extension of the POLYMOD study [1,2], which measured the number of daily contacts between participants of different age groups. The aim of CoMix was to assess how social mixing behaviour changed in the acute phase of the pandemic. The CoMix questionnaire was rapidly implemented first in the United Kingdom (UK), followed by Belgium and the Netherlands and, as a third stage, in over 20 countries in the EU/EEA, yielding unparalleled insight into how people changed their everyday lives in response to the real or perceived risk during a pandemic. For a timeline of the implementation of the CoMix questionnaire across the various countries, see Verelst et al .
The development and piloting of the CoMix questionnaire built on questions of the POLYMOD questionnaire as described in Mossong et al. , which contains an exemplary POLYMOD social contact diary as an attachment. The original CoMix questionnaire used in the UK was made publicly available as an attachment to the work of Gimma et al. . For an overview of funding sources used for CoMix data collection in various countries, see Verelst et al . For the CoMix data collection in the various European countries, the questionnaire was later updated to accommodate changes in vaccination and testing policies, and was translated into the national languages of all the participating countries and reviewed by local partners for language and cultural appropriateness.
In 2022, the CoMix survey was conducted again to enhance our understanding of contact mixing during the transition period beyond the acute phase of the COVID-19 pandemic. The questionnaire was further modified to accommodate booster vaccination and new types of tests, and incorporated additional feedback from social behaviour experts. The second round of CoMix covered nine countries (Austria, Belgium, Denmark, Italy, Estonia, Poland, Greece, Portugal, and Croatia).
The social contact data resulting from the survey can be accessed openly:
The questionnaire for the second round of CoMix (available above) can be accessed openly.
License for reuse: CC-BY-4.0.
References to related scientific publications
 Mossong, Joël, et al. Social contacts and mixing patterns relevant to the spread of infectious diseases. PLoS Medicine 5.3 (2008): e74.
 Prem, Kiesha, Alex R. Cook, and Mark Jit. Projecting social contact matrices in 152 countries using contact surveys and demographic data. PLoS Computational Biology 13.9 (2017): e1005697.
 Verelst, Frederik, et al. SOCRATES-CoMix: a platform for timely and open-source contact mixing data during and in between COVID-19 surges and interventions in over 20 European countries. BMC Medicine 19.1 (2021): 1-7.
 Gimma, Amy, et al. Changes in social contacts in England during the COVID-19 pandemic between March 2020 and March 2021 as measured by the CoMix survey: A repeated cross-sectional study. PLoS Medicine 19.3 (2022): e1003907.