Social contact patterns following the COVID-19 pandemic: a snapshot of post-pandemic behaviour from the CoMix study

Background The COVID-19 pandemic led to unprecedented changes in behaviour. To estimate if these persisted a final new round of the CoMix survey was conducted in four countries at a time when all societal restrictions had been lifted for several months. Methods We conducted a survey on a nationally representative sample in the UK, Netherlands (NL), Belgium (BE), and Switzerland (CH). Participants were asked about their contacts and behaviours on the previous day. We calculated contact matrices and compared the contact levels to a pre-pandemic baseline to estimate R. Results Data collection occurred from 17 November to 7 December 2022. 7,477 participants were recruited. Some were asked to undertake the survey on behalf of their children. Only 14.4% of all participants reported wearing a facemask on the previous day, varying between 6.7% in NL to 17.8% in CH. Self-reported vaccination rates in adults were similar for each country at around 86%. Trimmed mean recorded contacts were highest in NL with 9.9 (95% confidence interval [CI] 9.0 to 10.8) contacts per person per day and lowest in CH at 6.0 (95% CI 5.4 to 6.6). The number of contacts at home were similar between the countries. Contacts at work were lowest in the UK (1.4 contacts per person per day) and highest in NL at 2.8 contacts per person per day. Other contacts were also lower in the UK at 1.6 per person per day (95% CI 1.4 to 1.9) and highest in NL at 3.4 recorded per person per day (95% CI 4.0 to 4.0). Using the next-generation approach suggests that R for a close-contact disease would be roughly half pre-pandemic levels in the UK, 80% in NL and intermediate in the other two countries. Conclusions The pandemic appears to have resulted in lasting changes in contact patterns that would be expected to have an impact on the epidemiology of many different pathogens. Further post-pandemic surveys are necessary to confirm this finding. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The EU have been the primary funder for this study. Over the course of the study CoMix received funding from: EU Horizon 2020 Research and Innovations Programme - project EpiPose (Epidemic Intelligence to Minimize COVID-19's Public Health, Societal and Economical Impact, No 101003688); Medical Research Council (MC\_PC\_19065); the NIHR (CV220-088 - COMIX); HPRU in Modelling & Health Economics (NIHR200908); and UKHSA. This work reflects only the authors' view. The European Commission is not responsible for any use that may be made of the information it contains The following funding sources are acknowledged as providing funding for the named authors: CIJ received funding from the LSHTM COVID-19 response fund. DFID/Wellcome Trust (Epidemic Preparedness Coronavirus research programme 210758/Z/18/Z: JDM); The views expressed in this publication are those of the author(s) and not necessarily those of the NIHR or the UK Department of Health and Social Care NIHR (PR-OD-1017-20002: WJE). UK MRC (MC\_PC\_19065: WJE) ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: UK by the ethics committee of the London School of Hygiene & Tropical Medicine Reference number 21795 gave ethical approval for this work in the UK. The Ethics Committee of UZA with reference 3236 - BUN B3002020000054 gave ethical approval in Belgium. The Medical Research Ethics Committee (MREC) NedMec waived ethical approval the CoMix study in the Netherlands (research protocol number 22/917). The ethics committee of the Canton of Bern (project number 2020-02926) gave ethical approval for the CoMix data in Switzerland. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes The code and data used to conduct these analyses are found at https://github.com/jarvisc1/cmix\_post\_pandemic. * CI : confidence interval UK : United Kingdom CH : Switzerland BE : Belgium NL : Netherlands