Sample size in social contact surveys for epidemic modelling and risk prediction

Social contact surveys, measuring who contacts whom, are widely used for epidemic intelligence and public health decision-making. Despite their widespread use, sample size calculations are not performed. We conducted a review of social contact surveys (2008-2025) to characterise current practice. We characterised the impact of survey size on epidemic metrics using two social contact surveys, the UK Social Contact Survey and POLYMOD (Europe) and two methods. For each dataset and approach, we generated repeated subsamples and calculated the resulting reproduction numbers, characterised their distributions and measured uncertainty. We identified 107 unique social contact surveys from 57 studies. Sample sizes ranged from 30 to more than 10,000 participants, with a median of 1,438. One quarter of surveys contained fewer than 1,000 participants. Our analysis supports recruiting at least 1,000 participants for general-population social contact surveys used for epidemic modelling. Increasing sample size to 2,000 participants provides worthwhile gains in the precision of epidemic estimates, particularly for analyses using finer age stratification or individual-level approaches. Beyond approximately 3,000 participants, additional improvements in precision were small for the epidemic metrics analysed. This provides a practical balance between precision and participant burden.