Background: Most data on the effect of COVID-19 preventive measures relate to hospitalisations. We assessed how frequency of mild respiratory infections in children changed during the pandemic, analysing data from four years (9/2019?1/2023).

Methods: Data used are from the Swiss Paediatric Airway Cohort (SPAC), a prospective study of 0-16 year olds (at recruitment) visiting paediatric outpatient clinics. Parents completed a monthly online questionnaire for 1 year. We compared reported respiratory infections during the period 9/2019?03/2020 (preCOVID-19, no preventive measures (PMs)) with 9/2020?3/2021 (1st COVID-19 period, with PMs), 9/2021?3/2022 (2nd COVID-19 period, with PMs), and 9/2022?1/2023 (3rd COVID-19 period, no PMs). Accounting for age, sex, and repeated measurements, we used a multi-level logistic regression to compare the odds of respiratory infections (e.g., cold, infection of throat, nose, ears, or lungs) between periods.

Results: We received 3313 questionnaires, from 788 children, mean age 8 years (range 0-18), 58% male. 192 were completed preCOVID-19, 926, 1207, and 988 during the three COVID-19 periods respectively. Average number of infections was 8 per 100 per month preCOVID-19, and 5, 6, and 11 during the COVID-19 periods. Compared to baseline, respiratory infections were less common in the 1st and 2nd COVID-19 periods (OR: 0.3, 95%CI 0.2-0.5; OR: 0.5, 95%CI 0.3-0.8), but not during the 3rd period (OR: 0.9, 95%CI 0.6 - 1.4).

Conclusion: While respiratory infections were much less common during the first two pandemic years, incidence went back to normal when preventive measures were stopped, illustrating the impact of simple measures on occurrence of common colds.