This study surveyed adults’ behavior in the UK during a period of stringent physical distancing (“lockdown”) and compared the results to previously collected data. They found a large reduction in daily contacts particularly outside the home, resulting in a marked reduction in the estimated reproduction number from 2.6 to 0.62 (95% bootstrapped confidence interval [CI] 0.37 – 0.89).

Many countries have adopted unprecedented physical distancing policies in response to the COVID-19 pandemic. In an attempt to mitigate the impact, the UK implemented strict physical distancing measures instructing individuals to stay at home and avoid leaving their house except for essential work, to take one form of exercise a day, and to buy essential items such as food and medicines. In addition, sporting events, schools, restaurants, bars, gyms and other leisure or hospitality-related businesses have all been closed.

In this study, the authors evaluate whether these measures might be sufficient to control the epidemic by estimating their impact on the reproduction number (R₀, the average number of secondary cases generated per case in a completely susceptible population). They conducted a survey among 1,356 UK adults (referred to here as the CoMix survey), for which the first surveys were completed on Tuesday 24th March, one day after the UK lockdown was announced.

Participants reported the total number of direct contacts that they had on the day before the survey, which are people with whom they had at least a brief face-to-face conversation, or with whom they had any sort of skin-to-skin contact. These responses were compared similar data collected in 2006.

The authors found a 73% reduction in the average daily number of contacts observed per participant. This would be sufficient to reduce R₀ from a value from 2.6 before the lockdown to 0.62 (0.37 – 0.89) during the lockdown.

These findings indicate that physical distancing interventions are effective in reducing the spread of the SARS-CoV-2 virus, and should lead to a substantial impact and decline in cases in the coming weeks. However, this projected decline in incidence will not occur immediately due to significant delays between infection, onset of symptomatic disease and hospitalization, and reporting of these events.