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Time trends in social contacts of individuals according to comorbidity and vaccination status, before and during the COVID-19 pandemic: repeated cross-sectional population-based surveys

Objectives: To describe time trends in social contacts of individuals according to comorbidity and vaccination status before and during the first three waves of the COVID-19 pandemic in Quebec, Canada. Design: Repeated cross-sectional population-based surveys. Setting: General population. Participants: Non-institutionalized adults from Quebec, Canada, recruited by random digit dialling before (2018/2019) and during the pandemic (April 2020 to July 2021). A total of 1441 and 5185 participants with and without comorbidities, respectively, were included in the analyses. Main outcome measures: Number of social contacts (two-way conversation at a distance [≤]2 meters or a physical contact, irrespective of masking) documented in a self-administered web-based questionnaire. We compared the mean number of contacts according to the comorbidity status of participants (pre-existing medical conditions with symptoms/medication in the past 12 months) and 1-dose vaccination status during the third wave. All analyses were performed using weighted generalized linear models with a Poisson distribution and robust variance. Results: Contacts significantly decreased from a mean of 6.1 (95% confidence interval 4.9 to 7.3) before the pandemic to 3.2 (2.5 to 3.9) during the first wave among individuals with comorbidities, and from 8.1 (7.3 to 9.0) to 2.7 (2.2 to 3.2) among individuals without comorbidities. Individuals with comorbidities maintained fewer contacts than those without comorbidities in the second wave, with a significant difference before the Christmas 2020/2021 holidays (2.9 (2.5 to 3.2) v 3.9 (3.5 to 4.3); P<0.001). During the third wave, contacts were similar for individuals with (4.1, 3.4 to 4.7) and without comorbidities (4.5, 4.1 to 4.9; P=0.27). This could be partly explained by individuals with comorbidities vaccinated with their first dose who increased their contacts to the level of those without comorbidities. Conclusions: The lower level of contacts maintained by individuals with comorbidities could have influenced the burden of hospitalisations and deaths of the second wave in Quebec. It will be important to closely monitor COVID-19-related outcomes and social contacts by comorbidity and vaccination status to inform targeted or population-based interventions.