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

ABSTRACT

Background: The COVID-19 pandemic has significantly affected social contact patterns worldwide. Particularly during the first epidemic wave, because of the lack of specific treatment or vaccine, most countries around the world enforced non-pharmaceutical interventions. Italy was one of the first countries to be strongly affected by the pandemic, imposing in the first epidemic wave a hard lockdown. During the second wave, the country implemented color-coded, progressively restrictive tiers at the regional level according to weekly epidemiological risk assessments. Methods: We analyze longitudinal surveys of a representative sample of the Italian population by age, gender, and region of residence, collected during the second epidemic wave. After presenting a statistical description of the sample, we compare variations in contact patterns according to a color-coded tier of interventions experienced by the participants. In particular, we use contact matrices to quantify the reduction in the number of contacts by age group and contact settings, focusing on the adult population. We also compare the results with the pre-pandemic baseline assessing the impact of tiered restrictions on contacts. Finally, we compute the reproduction number to evaluate the impact of the restrictions on the spreading of the disease.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. Moreover, we show that the 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: We showed that the progressive restriction tiers implemented in Italy reduced overall the reproduction number, with stricter interventions associated with higher reductions. Readily collected contact data can promptly inform the implementation of mitigation measures at the national level in epidemic emergencies to come.