2.1 Data Source
We searched PubMed, Embase, and Cochrane Library for the update articles published from the inception of each database to Jun 1, 2021. when duplicate publications were identified, we chose the most complete and recent trial . Two investigators (Z.Y. and X.W.) independently retrieved all the related studies in the databases and excluded duplicate publications. The combined text and medical subject heading (MeSH) terms were cross-searched using MeSH and free word as follows: ( Asthma[Mesh] OR allergic asthma[Title/Abstract] OR Bronchial Asthma[Title/Abstract]) AND Control[Title/Abstract]) AND (COVID-19[Mesh] OR COVID-19 Virus Disease[Title/Abstract] OR COVID-19 Virus Infection[Title/Abstract] OR 2019-nCoV Infection[Title/Abstract] OR Coronavirus Disease-19[Title/Abstract] OR 2019 Novel Coronavirus Disease[Title/Abstract] OR 2019-nCoV Disease[Title/Abstract] OR SARS Coronavirus 2 Infection[Title/Abstract] OR SARS-CoV-2 Infection[Title/Abstract] OR (COVID-19 Pandemic[Title/Abstract]) AND (Child[Mesh] OR Children[Title/Abstract]). We also reviewed abstracts and presentations from major conference proceedings up to Jun 1, 2021 to ensure that no additional studies were overlooked.