Impact of tiered measures on social contact and mixing patterns of in Italy during the second wave of COVID-19

Abstract

Background Most countries around the world enforced non-pharmaceutical interventions against COVID-19. Italy was one of the first countries to be affected by the pandemic, imposing a hard lockdown, in the first epidemic wave. During the second wave, the country implemented progressively restrictive tiers at the regional level according to weekly epidemiological risk assessments. This paper quantifies the impact of these restrictions on contacts and on the reproduction number. Methods Representative (with respect to age, sex, and region of residence) longitudinal surveys of the Italian population were undertaken during the second epidemic wave. Epidemiologically relevant contact patterns were measured and compared with pre-pandemic levels and according to the level of interventions experienced by the participants. Contact matrices were used to quantify the reduction in the number of contacts by age group and contact setting. The reproduction number was estimated to evaluate the impact of restrictions on the spread of COVID-19. Results The comparison with the pre-pandemic baseline shows a significant decrease in the number of contacts, independently from the age group or contact settings. This decrease in the number of contacts significantly depends on the strictness of the non-pharmaceutical interventions. For all levels of strictness considered, the reduction in social mixing results in a reproduction number smaller than one. In particular, the impact of the restriction on the number of contacts decreases with the severity of the interventions. Conclusions The progressive restriction tiers implemented in Italy reduced the reproduction number, with stricter interventions associated with higher reductions. Readily collected contact data can inform the implementation of mitigation measures at the national level in epidemic emergencies to come.

Modeling the interplay between disease spread, behaviors, and disease perception with a data-driven approach

“…We first stratify the population into seven age groups (0-4, 5-17, 18-29, 30-39, 40-49, 50-59, and 60+), using data about the population distribution in Italy across the various age groups from the 2019 United Nations World Population Prospects [35]. We then use the data from the CoMix survey for Italy to generate two contact matrices: the one resulting from data collected in the red zone is used in the model to reflect the contacts of individuals who adopt protective behaviors (named in the rest of the paper as "compliant" individuals), while we use the one built from the yellow zone data to describe the contacts of what we call "non-compliant" individuals (see [36] for more detailed information on the specific top-down restrictions imposed by health authorities during the data collection).…”

“…In addition to questions related to their contacts (e.g. total number, frequency, location, etc.see [36] for detailed information on the contact surveys), participants over 18 years old answered questions related to their risk perception. Concerning perceived severity, participants were asked to indicate their agreement with the statement "Coronavirus would be a serious illness for me" using a 5-point Likert scale ranging from strongly disagree to strongly agree.…”

Repetition in Social Contact Interactions: Implications in Modelling the Transmission of Respiratory Infectious Diseases in Pre-pandemic & Pandemic Settings

“…Numerous studies similar in setup have been conducted in different countries in both pre-pandemic and pandemic periods [4]. The CoMix study is the largest study across Europe gathering social contact data aiming to assess changes in contact behaviour during the pandemic [2,[6][7][8][9][10][11]. The information from these surveys has proven invaluable in informing transmission dynamics within mathematical models including network models [12], agent-based models [13], and compartmental models [14][15][16].…”

Is a tiered restrictions system an effective intervention for COVID-19 control? Results from Portugal, November-December 2020

“…The evidence available, from other European countries, on the impact of similar tiered restrictions systems on COVID-19 transmissibility suggests a decrease in the effective reproduction number R(t) in all tiers, with a larger decrease of COVID-19 cases in tiers with stricter measures [ 7 , 8 , 15 – 18 ], compared to those with less strict ones. The Italian tiered system was a progressive colour-coded system implemented on a regional basis, where tiers were based on the combination of 21 quantitative indicators on the level of transmission, the burden on older age groups and healthcare, and the resilience of monitoring systems [ 18 , 19 ]. This study showed that this tiered system decreased human activities [ 7 ], namely time spent outside home, public transportation, recreational and retail activities and also decreased contacts [ 18 ], with stricter tiers showing a higher decrease.…”

“…The Italian tiered system was a progressive colour-coded system implemented on a regional basis, where tiers were based on the combination of 21 quantitative indicators on the level of transmission, the burden on older age groups and healthcare, and the resilience of monitoring systems [ 18 , 19 ]. This study showed that this tiered system decreased human activities [ 7 ], namely time spent outside home, public transportation, recreational and retail activities and also decreased contacts [ 18 ], with stricter tiers showing a higher decrease. However, the decrease in the time spent outside home observed in all tiers was below the values observed during the lockdown [ 7 ].…”