Social mixing patterns in the UK following the relaxation of COVID-19 pandemic restrictions, July–August 2020: a cross-sectional online survey

Objectives To quantify and characterise non-household contact and to identify the effect of shielding and isolating on contact patterns. Design Cross-sectional study. Setting and participants Anyone living in the UK was eligible to take part in the study. We recorded 5143 responses to the online questionnaire between 28 July 2020 and 14 August 2020. Outcome measures Our primary outcome was the daily non-household contact rate of participants. Secondary outcomes were propensity to leave home over a 7 day period, whether contacts had occurred indoors or outdoors locations visited, the furthest distance travelled from home, ability to socially distance and membership of support bubble. Results The mean rate of non-household contacts per person was 2.9 d-1. Participants attending a workplace (adjusted incidence rate ratio (aIRR) 3.33, 95% CI 3.02 to 3.66), self-employed (aIRR 1.63, 95% CI 1.43 to 1.87) or working in healthcare (aIRR 5.10, 95% CI 4.29 to 6.10) reported significantly higher non-household contact rates than those working from home. Participants self-isolating as a precaution or following Test and Trace instructions had a lower non-household contact rate than those not self-isolating (aIRR 0.58, 95% CI 0.43 to 0.79). We found limited evidence that those shielding had reduced non-household contacts compared with non-shielders. Conclusion The daily rate of non-household interactions remained lower than prepandemic levels measured by other studies, suggesting continued adherence to social distancing guidelines. Individuals attending a workplace in-person or employed as healthcare professionals were less likely to maintain social distance and had a higher non-household contact rate, possibly increasing their infection risk. Shielding and self-isolating individuals required greater support to enable them to follow the government guidelines and reduce non-household contact and therefore their risk of infection.


GENERAL COMMENTS
This well-done work provides highly valuable quantitative measurement on social mixing patterns in UK. I have only two minor suggestions: 1. Actually, the UK relaxed pandemic restriction twice, in 2020 and 2021, respectively. Therefore, the title should specify the timing of measurement. For example: "Social mixing pattern in the UK following the relaxation of COVID-19 pandemic restriction, July to August 2020: a cross-sectional online survey".

2.
A major concern is the claim (in conclusion and the first paragraph of discussion) that "the daily rate of non-household interactions remain lower than pre-pandemic levels", using prepandemic POLYMOD study (2005)(2006) as the reference. I am not sure whether participants and survey methods are sufficiently similar between the two studies to allow the authors made such claim. Try to transparently specify the finding as "...lower than prepandemic levels measured in the POLYMOD study (2005)(2006),..." and address the potential difference in participants and survey methods in the limitation section.

GENERAL COMMENTS
The manuscript introduces the study objective, the analysis and the results in a clear and comprehensive way. My only, minor, suggestion is to link its results to similar studies carried out in Europe and worldwide. To this end, a rapid review on social contact patterns during the COVID-19 pandemic (Liu et al, Epidemiology, 2021) and a study performed in Belgium during the same period and a similar epidemiological situation (Coletti et al, Scientific Reports, 2021) could help an interested reader to put the results in perspective. This is indeed a suggestion, as the paper links the results of the study mostly to other studies in the UK, with only a comparison with Luxembourg being included. I think this manuscript presents the study in a complete way, allowing for reproducing its results. The statistical analysis is sound and fully documented. I therefore think this paper should be accepted.

Reviewer 1
Prof. Chi-Tai Fang, National Taiwan University Comments to the Author: This well-done work provides highly valuable quantitative measurement on social mixing patterns in UK. I have only two minor suggestions: We thank the reviewer for taking the time respond to our manuscript and for the positive feedback.
Actually, the UK relaxed pandemic restriction twice, in 2020 and 2021, respectively. Therefore, the title should specify the timing of measurement. For example: "Social mixing pattern in the UK following the relaxation of COVID-19 pandemic restriction, July to August 2020: a crosssectional online survey".
We thank the reviewer for this suggestion. We have changed the title to 'Social mixing pattern in the UK following the relaxation of COVID-19 pandemic restriction, July to August 2020: a cross-sectional online survey' to better reflect the study period (lines 1-3).
A major concern is the claim (in conclusion and the first paragraph of discussion) that "the daily rate of non-household interactions remain lower than pre-pandemic levels", using prepandemic POLYMOD study (2005)(2006) as the reference. I am not sure whether participants and survey methods are sufficiently similar between the two studies to allow the authors made such claim. Try to transparently specify the finding as "...lower than pre-pandemic levels measured in the POLYMOD study (2005)(2006),..." and address the potential difference in participants and survey methods in the limitation section.
We thank the reviewer for this comment.
We have acknowledged the potential differences in study population and design of pre-pandemic contact studies as a limitation in the discussion. 'Comparisons to pre-pandemic contact levels in the UK are based on social contact studies conducted within the UK prior to 2020, however, these are subject to differences in study population and study design in particular sample distributions and data collection methods.' (lines 362-365).