Table 1. Characteristics and details of the included studies.

Studies	Study design	Location	Sample sizeb	Risk factors included																			Analysis in this study
				A		P		O		D		L		C		N		G		I		H
Zachariah et al. (2020) 17	R/CS	USA	50																				SR & MA
Chao et al. (2020) 26	R/CS	USA	67																				SR & MA
Swann et al. (2020) 21	P/CO	UK	580																				SR & MA
Götzinger et al. (2020) 20	A/CO	Europe	582																				SR & MA
Bellino et al. (2020) 16	R/CO	Italy	3,836																				SR & MA
Fisler et al. (2020) 31	R/CO	USA	77																				SR & MA
Ouldali et al. (2021) 13	P/CS	France	397																				SR & MA
Graff et al. (2021) 18	R/CS	USA	454																				SR & MA
Kompaniyets et al. (2021) 24	R/CS	USA	43,465																				SR & MA
Verma et al. (2021) 27	R/CO	USA	82																				SR & MA
Mithal et al. (2020) 19	CC	USA	18																				SR
Kanburoglu et al. (2020) 22	P/CO	Turkey	37																				SR
Wardell et al. (2020) 23	CC	USA	4																				SR
Cardona-Hernandez et al. (2021) 25	R/CO	Multinationala	16																				SR
Dannan et al. (2020) 28	CC	UAE	5																				SR
Madhusoodhan et al. (2021) 29	R/CS	USA	98																				SR
Barhoom et al. (2021) 30	CC	Iran	4																				SR

A = age, P = prematurity, O = obesity, D = diabetes, L = chronic lung disease, C = cardiac disease, N = neurologic disease, G = complex genetic disease, I = immune-compromising disorder and/or immunosuppressive medication, H = hemato-oncologic disease, R/CS = retrospective cross-sectional, P/CO = prospective cohort, A/CO = ambispective cohort, R/CO = retrospective cohort, P/CS = prospective cross-sectional, CC = case series, SR = systematic review, MA = meta-analysis.

^aChina, Italy, Spain, and USA; ^bNumber of enrolled children.