To assess the transmissibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in households with children and to assess whether asthma is a risk factor for infection.

Over a 6-month period from May 2020 to February 2021, in 1394 households with children with asthma and allergic diseases (including 1978 caregivers, among whom 439 had a diagnosis of asthma, and 2164 children, among whom 711 had a diagnosis of asthma), every other week nasal swabs were obtained for polymerase chain reaction testing for SARS-CoV-2. Weekly surveys were completed regarding infection symptoms and, if present, additional PCR testing was done of all household members.

Of participants, 261 in 147 households tested positive for SARS-CoV-2. The positivity rate was higher for illness-triggered tests (6.3%) than for the surveillance tests (0.97%). The household infection probability was 25.8%. The individual probability of infection was 14.0%, and was similar between children, teens, and adults. Infections were symptomatic in 24.5% of children, 41.2% of teenagers, and 62.5% of adults. Asthma was not associated with infection risk (adjusted hazard ratio = 1.04 [95% confidence interval (CI) = 0.73–1.46]). The household secondary attack rate was 57.7%. Exposure to a symptomatic household member was associated with an 87.39-fold increase in infection risk (95% CI = 58.02–131.63), whereas exposure to an asymptomatically infected household member was associated with a 27.80-fold increase in risk (95% CI = 17.16–45.03).

“Asthma does not increase the risk of SARS-CoV-2 infection.”

This study was conducted in the early days of the coronavirus disease 2019 pandemic largely before the widespread use of vaccines and before the evolution of subsequent viral variants, yet provides important information regarding the transmissibility of SARS-CoV-2. Although children, teens, and adults were equally likely to become infected, children were much more likely to have asymptomatic, but still transmissible, infection. The study was conducted in households enriched for asthma, and found that patients with asthma were no more likely to be infected with SARS-CoV-2. This finding, replicated in other studies, has been surprising given that other studies have shown that the bronchial epithelium from patients with asthma has impaired antiviral responses. There were too few patients with severe infection in this study for analysis, but most other studies have found (again surprisingly) that asthma is not a risk factor for severe disease.