Table 1. Patient characteristics in the included studies.

	No. of Subjects	AgeMean (range)	GenderFemale/Male	APACHEII score - mean (range)	Site of infection	Survival/Death	Length of follow-up
Severe influenza infection	4	33 (21–48)	3/1	14 (13,17)	Lung	4/0	5 days
Severe bacterial pneumonia	6	63 (52–75)	3/3	22 (10,33)	Lung	4/2	5 days
Mild influenza infection	9	NA	NA	NA	Lung	9/0	3.5 days
Post-vaccination subjects	18	43 (24–70)	12/6	NA	NA	18/0	7 days
Healthy controls	18	43 (24–70)	12/6	NA	NA	18/0	1 day

APACHE denotes Acute Physiology and Chronic Health Evaluation II scores. NA denotes not available or not applicable.