Respiratory morbidity before and during the COVID-19 pandemic from birth to 18 months in a Swedish birth cohort.

Background: Respiratory infections in early life are an identified risk factor for asthma. We hypothesized that infection-prevention measures during the coronavirus disease 2019 (COVID-19) pandemic influenced the risk of respiratory morbidity and aeroallergen sensitization in early childhood.

Objective: We compared respiratory morbidity and aeroallergen sensitization in children born before and during the pandemic.

Methods: We compared a COVID-19 category (exposed children; n = 1661) to a pre-COVID-19 category (nonexposed children; n = 1676) by using data from the prospective population-based NorthPop Birth Cohort study in Sweden. Data on respiratory morbidity and concomitant medication were retrieved from national registers. Prospectively collected data on respiratory morbidity using web-based questionnaires at 9 and 18 months of age were applied. At age 18 months, serum IgE levels to aeroallergens were determined (n = 1702).

Results: The risk of developing any respiratory tract infection (adjusted odds ratio [aOR] = 0.33 [95% CI, 0.26-0.42]), bronchitis (aOR = 0.50 [95% CI, 0.27-0.95]) and croup (aOR = 0.59 [95% CI, 0.37-0.94]) were decreased in the COVID-19 category. The risk of wheeze in the first 9 months was lower in the COVID-19 category (aOR = 0.70 [95% CI, 0.55-0.89]). There were also fewer prescriptions of antibiotics in the COVID-19 category. The prevalence of aeroallergen sensitization was similar between categories.

Conclusion: Children born during the COVID-19 pandemic demonstrated significantly decreased risks of respiratory infections and prescribed antibiotics until 18 months of age compared to children born before the COVID-19 pandemic. Whether this will affect the risk of developing asthma in childhood is being followed.