# The role of frailty in shaping social contact patterns in Belgium, 2022–2023

## TL;DR

This study explores how frailty affects social contact patterns in Belgium, showing that accounting for frailty improves understanding of disease transmission and intervention effectiveness.

## Contribution

The study introduces frailty-dependent contact matrices and a mathematical model integrating frailty levels to better predict epidemic dynamics.

## Key findings

- Frail individuals report fewer daily contacts compared to non-frail individuals.
- Incorporating frailty into models significantly changes epidemic curve predictions.
- Contact patterns vary by age and frailty, influencing transmission dynamics.

## Abstract

Social contact data are essential for understanding the spread of respiratory infectious diseases and designing effective prevention strategies. However, many studies often overlook the heterogeneity in mixing patterns among older age groups and individual frailty levels, assuming homogeneity across these sub-populations. This shortcoming may undermine non-pharmaceutical interventions by not targeting specific contact behaviours, potentially reducing their effectiveness in controlling disease. To address this gap, we conducted a contact survey in Flanders, Belgium (June 2022–June 2023). We collected data from 5995 participants (overall response rates of 19.34%) who recorded 31,375 contacts with distinct individuals. Within this cohort, 14.50% were classified as frail, and 46.85% were classified as non-frail. On average, participants report 5.48 contacts daily, with a median of 4 contacts (IQR: 2–7). These contacts vary based on participants’ age and frailty levels, influenced by the locations of their interactions. Using the collected data, we reconstructed frailty-dependent contact matrices and developed a contact-based mathematical model that integrates participants’ and contactees’ frailty levels to investigate how frailty levels affect transmission dynamics. Incorporating frailty levels into the mathematical model substantially alters the shape of epidemic curves and peak incidences. Such insights might provide useful insights for informing non-pharmaceutical interventions, indicating the potential benefit of similar data collection in different countries.

The online version contains supplementary material available at 10.1038/s41598-025-96662-8.