Study	Reason for exclusion
Alshami 2018	Wrong study design ‐ review article
Arabi 2020	Wrong study design ‐ review article
Beinert 2000	Wrong study design ‐ review article
Carr 2017	Wrong study design ‐ review article
Ceccato 2018	Wrong study design ‐ review article
Glazebrook 1942	Wrong study design ‐ the study design was not appropriate since the study recruited new participants in the middle of the study
Hemilä 1997	Wrong study design ‐ review article
Hemilä 2003	Wrong study design ‐ correspondence
Hemilä 2007	Wrong study design ‐ review article
Hemilä 2008	Wrong study design ‐ correspondence
Hemilä 2011	Wrong study design ‐ letter to the editor
Hunt 1984	Wrong population ‐ the study included hospitalised geriatric patients with any diagnosis
Jain 2002	Wrong intervention ‐ the study provided multiple micronutrient supplement
Kim 2018	Wrong study design ‐ cohort study
Klenner 1948	Wrong study design ‐ no comparison group
Mahalanabis 2006a	Wrong intervention ‐ intervention included co‐supplementation of alpha‐tocopherol and vitamin C
Mahalanabis 2006b	Wrong study design ‐ letter to the editor
NCT02186158	Wrong population ‐ the study included participants with hospital‐acquired pneumonia
Ogal 2019	Wrong intervention ‐ the intervention includes provision of echinacea
Socci 2012	Wrong intervention ‐ the intervention included co‐administration of immunotherapy with oral bacterial lysates and vitamin C