Social contact patterns during the COVID-19 pandemic in 21 European countries – evidence from a two-year study

COVID-19 primarily spreads via aerosols and thus through close, direct, and in-person social contacts. Especially at the start of the COVID-19 pandemic, when there were no effective vaccines and treatments, the spread of the disease was mostly managed by promoting non-pharmaceutical interventions (NPIs), which served to avoid potential exposure to the pathogen in the population [1].

In Europe, Italy was the first country to begin major NPIs. On March 9 2020, the country issued their first national lockdown mandating 60 million residents to stay at home [2]. On March 14, the Spanish government declared a state of emergency [3]. Similar announcement emerged in other European countries soon thereafter [4]. Lockdown mandates posed immediate restrictions on social contacts. Contact surveys conducted quickly after these measures showed that the number of mean daily contacts per person rapidly fell from pre-pandemic levels to approximately 4 per person in Belgium, Italy, Netherlands, Germany, United Kingdom (UK), France, Greece, and Luxembourg [5‐10].

Many countries in the region began to ease restrictions during the summer of 2020 and continued to vary the intensities of various NPIs to control the epidemic in the two years that followed. Although contacts curbed when restrictions were introduced, commensurate rises in social contacts were not seen when measures were lifted. In the UK, for instance, at its highest recorded level, the mean number of contacts in 2021 only returned to approximately 50% of that observed in pre-pandemic times (as measured in the POLYMOD contact survey study in 2005 to 2006 [11]) [12]. Social contact behaviours during the pandemic have been shown to vary by population and demographics [12, 13]. In addition to the guidance issued by the authorities, individuals may also have adopted new behaviours to avoid pathogen exposure for other reasons, e.g., personal circumstances such as risk profile, perceived pandemic threat level, work requirements, among others [14]. Research opportunities into the complexity and determinants of changes in social contacts have thus far been relatively limited.

We conducted a multi-country study in the European region, following individuals in real-time over the course of the COVID-19 pandemic. We aimed to assess social contacts in 21 European countries between March 2020 and March 2022 using a large dataset. We present descriptive analyses showing the mean number of contacts reported by study participants, and how these changed over time across the study countries. We also examine the potential determinants influencing the mean number of contacts.

The CoMix study collected data in 21 European countries between March 2020 and March 2022 (Fig. 1). Except for the beginning and the end of the study, at least 10,000 survey responses were recorded across all participating countries on a monthly basis. At the highest point in January 2021, the number of survey responses recorded reached 37,808 in 14 countries.

Data was collected from 96,456 adults, who made a total of 463,336 responses to the CoMix survey (Table 1). Of these, 47% (217,500) took place in the UK. Approximately 20% of the survey responses were given by participants aged between 40 and 59 years.

Altogether, 19.3% of responses were provided by participants living with at least one other person aged 65 years or above. This proportion ranged between 14.5% in Switzerland and 33.2% in Italy (Supplementary Material II). Mean household size ranged between 2.0 people in Finland to 3.0 people in Poland (Supplementary Material II). Risk perception also differed between countries. The percentage reporting “strongly agree” to “I am likely to catch coronavirus” averaged 5.3%, and ranged between 2.1% in Finland and 23.5% in Lithuania. About 10–25% were concerned about getting serious symptoms from coronavirus; and about 10–55% were concerned about spreading coronavirus to someone vulnerable.

Across all survey responses, self-reported usage of face-covering was 64.0%—lowest in the Netherlands (34.3%) and almost universal at 95% in Malta. Between < 5% and 60% of survey responses were reported by partially or fully vaccinated participants. Approximately 20–40% of survey responses were reported by participants who self-identified as having at least one high-risk condition. Presentation of symptoms was reported in about one quarter of survey responses. The most common symptom was headache or body ache (14.9%).

To our knowledge, this study on social contact during the pandemic has been the largest of its kind in terms of the number of countries, participants, and observations included. The CoMix survey, collecting standardized repeated cross-sectional data, facilitated an examination of social contacts across 21 European countries over a 24-month period, and assessments of contact rates before and during COVID-19 using established findings.

More than 460,000 survey responses were considered in the current analysis. In all examined countries in the region, despite changes in NPIs, mean contact rates remained low over the study period. In the subset of countries where data were available, mean contact rates were much lower than pre-pandemic levels, predominately due to fewer contacts not at home. NPIs showed clear immediate effects far beyond the time when many different restrictions were lifted. The relationships between individual perceptions or national policy determining contacts varied across the countries studied.

Easing, or partial easing, of the first round of major NPIs began in May 2020 in the countries represented in this study. Much of the increase in social contacts around that time was largely based on more contacts at work [16]. Findings from our study across different countries confirmed that containment measures at workplaces and stay-at-home orders were both, by and large, associated with fewer contacts in the population, though some important exceptions were observed. These variations might be explained by the adoption of any tiered approaches to NPI implementation, behaviour of the populations, and rigors of rules enforcement [24]. Following the lifting of restrictions, the initial increases in work contacts were relatively slow, and possibly influenced by sector of employment, availability of face covering, and other adjustments enabling the return to the workplace. The pandemic has resulted in changes to the working arrangements of many who are now based at home and may continue to work at home, in some capacity, for the foreseeable future. In this study, we also found lower contacts in non-work settings under workplace closure mandates, suggesting potential wider effects on social contacts outside of work. Conversations at work with colleagues may offer opportunities for social connections beyond work, and the shift to homeworking potentially reduces the number of opportunities for these spontaneous interactions [25]. The full consequences of working at home on social contacts, especially the unintended, knock-on effect in non-work related social contacts (e.g. increased risk of feeling lonely [26]), are yet to be carefully examined.

Our study also identified a link between contacts at home and concerns about spreading COVID-19 to vulnerable persons. Such perception was not observed for contacts outside the home. Whilst measures focused on social distancing behaviours can be undertaken to reduce the spread of COVID-19 within the community, people with symptoms of the virus were instructed or advised to remain in their homes. Within-household contacts are thought to be the dominant route of disease spread when extensive community control measures are in place [27]. Despite guidance advising household members to socially distance, individuals are likely to interact repeatedly. Those living with household members who are older, have underlying medical conditions, or share a bed might be particularly concerned [28‐30]. Strategies to support people quarantining at home with other household members remain vital in the ongoing pandemic.

Whilst we set out to identify determinants of social contacts, our study – observational in nature – might have picked up on other correlates of social contacts. In most countries, presentation of symptoms, use of face-covering, vaccination against COVID-19, and concerns about infection (but not getting severely ill) showed associations with more contacts in non-home settings. People who had more contacts likely had a greater tendency to acquire COVID-19, were concerned about it, and might have adopted the behaviour of using face-covering – or had to wear one to go to work, and to travel on public transport. Our finding on greater use of face-covering aligns with previous studies in the US [31] and Japan [32] showing masks-wearing was more prominent among individuals who were more socially integrated and who spent less time at home, including going to commercial locations and restaurants.

The current study offers important insights into the extent to which children meet others when they do not attend school. Whilst contact rates were lower when children did not go to school, they were still, on average, making contacts with more people than adult. Concerns as to grandparents or older people taking care of children when they are not at school have been raised [33]. Given that school closures are often accompanied by advice to parents to limit the contact their children have with others, further research into the characteristics of children’s contacts on days they do not go to school may be helpful in improving the advice that is given out.

Our findings should be interpreted with several limitations in mind. First, there were likely differences in the extent to which the NPIs were implemented in different countries. For instance, the allowable reasons to leave one’s home during periods of stay-at-home orders might vary across countries. Our measure on NPIs did not capture these variabilities, as well as any subnational differences. Second, CoMix data collection had different temporal coverages across the study countries, including periods of higher social activities such as end of year holiday period. We conducted analyses grouping countries with field work at similar times to partially account for the effect of time. Third, our grouping of countries based on timing of fieldwork might have put countries with different characteristics and measures together, thus potentially masking country-specific relationships. For instance, perception and acceptability towards mask usage across countries or cultures might vary, leading to different relationships with contact rates. Where data availability permitted, analysis at the level of individual country using the full model formulation was also performed to gain insight from comparing the differences between countries. Fourth, survey fatigue appeared substantial in our study. As contact surveys continue to be used as an important public health tool for emerging infectious disease, survey methodologies may need to be adjusted. Limiting the maximum number of survey response per participant, and using fewer, but strategically timed survey rounds may yield results that more accurately capture contact patterns in the population. In addition, efforts to minimize response bias is likey more important now than during pre-pandemic times – such as when POLYMOD was conducted – since the relationship between contacts and disease transmission has become more widely acknowledged in the population. Lastly, the effect of some covariates may be better uncovered with longitudinal models. For instance, individuals may make more contacts when they are vaccinated compared to before, but this overall effect could be masked by other covariates when the individual level of the data is not accounted for. Such changes are beyond the scope of the current paper, and might be better addressed at the level of individual person, with approaches such as paired measures [34].

The COVID-19 pandemic has led to an unprecedented global impact with wide ranging health and social consequences. Across 21 countries in the European region, we found that in-person contacts remained far below pre-pandemic levels throughout the two-year study period. In this multi-country analysis, we presented a detailed historical record of social behaviour during the COVID-19 pandemic, research insights on the influence of NPIs, the key roles of individuals’ perceived pandemic threat level, and personal circumstances, and insights the can be gained by comparing the differences between countries. Our study provides an account across different countries, and paves the way to develop future studies, coordinated at the regional level, to guide infectious diseases outbreak responses, particularly for a large-scale pandemic.