CoMix: comparing mixing patterns in the Belgian population during and after lockdown

Abstract

The COVID-19 pandemic has shown how a newly emergent communicable disease can lay considerable burden on public health. To avoid system collapse, governments have resorted to several social distancing measures. In Belgium, this included a lockdown and a following period of phased re-opening. A representative sample of Belgian adults was asked about their contact behaviour from mid-April to the beginning of August, during different stages of the intervention measures in Belgium. Use of personal protection equipment (face masks) and compliance to hygienic measures was also reported. We estimated the expected reproduction number computing the ratio of [Formula: see text] with respect to pre-pandemic data. During the first two waves (the first month) of the survey, the reduction in the average number of contacts was around 80% and was quite consistent across all age-classes. The average number of contacts increased over time, particularly for the younger age classes, still remaining significantly lower than pre-pandemic values. From the end of May to the end of July , the estimated reproduction number has a median value larger than one, although with a wide dispersion. Estimated [Formula: see text] fell below one again at the beginning of August. We have shown how a rapidly deployed survey can measure compliance to social distancing and assess its impact on COVID-19 spread. Monitoring the effectiveness of social distancing recommendations is of paramount importance to avoid further waves of COVID-19.

Figure 1

Contacts according to participant age class and dataset. Mean number of contacts broken down by participant age and dataset. For dataset coming from the CoMix survey, the starting date of the data collection is shown in brackets. Errorbars mark the 95% CI.

Figure 2

Home/away from home contacts. (a): Mean number of contacts at home. Errorbars mark the 95% CI.(b): Mean number of contacts away from home. Errorbars mark the 95% CI.

Figure 3

Social contact matrices. (a): Average number of daily reported contacts for the 2010 survey. (b–i) Average number of daily reported contacts for the 8 waves of the CoMix survey. The columns corresponding to participants below 18 years of age in the 2010 data have been removed, to ease the comparison with the CoMix data.

Figure 4

Reproduction number. (a,b): Reproduction number considering all contacts, without imputation (a) and with imputation of contacts for children (i.e. individuals <18y) (b).(c,d): Reproduction number considering physical contacts, without imputation (c) and with imputation of contacts for children (d). All values are obtained starting from a normally distributed ${\text{R}}_0$ ($\text{mean}=3.344$, $\text{sd}=0.028$) and the ratio of ${\text{R}}_0$ computed with respect to the 2010 survey data. The horizontal line marks a reproduction number of 1.

Figure 5

Percentage of participants using face mask. Average number of participants wearing mask broken down by age. Errorbars mark the 95% CI.

Figure 6

Calendar of interventions and CoMix wave data collections.

Figure 7

Percentage of participants having washed their hands. Average number of participants having washed their hands at least once in the last three hours, broken down by age. Errorbars mark the 95% CI.