Contact behaviour before, during and after the COVID-19 pandemic in the Netherlands: evidence from contact surveys in 2016-2017 and 2020-2023

Background The first wave of the COVID-19 pandemic in 2020 was largely mitigated by reducing contacts in the general population. In 2022 most contact-reducing measures were lifted. Aim We assess whether the population has reverted to pre-pandemic contact behaviour and how this would affect the transmission potential of a newly emerging pathogen. Methods The PIENTER Corona study was held every 2-6 months in the Netherlands from April 2020, as a follow-up on the 2016-2017 PIENTER3 study. In both studies, participants (ages 1-85) reported the number and age group of all face-to-face persons contacted on the previous day. The contact behaviour during and after the COVID-19 pandemic was compared to the pre-pandemic baseline. The transmission potential was examined using the Next Generation Matrix approach. Results We found an average of 15.4 (14.3-16.4, 95% CI) community contacts per person per day in the post-pandemic period, which is 13% lower than the baseline value of 17.8 (17.0-18.5). Children have the highest number of contacts as before the pandemic. Mainly adults aged 20-59 have not reverted to their pre-pandemic behaviour, possibly because this age group works more often from home. Although the number of contacts is structurally lower compared to the pre-pandemic period, the effect on the transmission potential of a newly emerging respiratory pathogen is limited if all age groups were equally susceptible. Conclusion Continuous monitoring of contacts can signal changes in contact patterns and can provide a ‘new normal’ baseline. Both aspects are needed to be prepared for a future pandemic.