*Most of these studies were excluded on the basis of multiple criteria.

Results favor treatment with convalescent blood products (z = 7.1; P < 0.001), and there was no statistical evidence of large heterogeneity (Q = 7.0; I² = 29.3%; P = 0.22). The pooled estimate should be interpreted with caution and should not be generalized to other strains of virulent influenza without further study. Percentages have been rounded to the nearest whole integer. *In 2 studies with low mortality rates in the treatment group, the majority of patients were treated within 48 hours after pneumonia complicating influenza was diagnosed (18, 23, 24). McGuire and Redden (23, 24) reported a range of mortality rates of 30% to 60% among controls, and 30% was used in the analysis.

Results favor treatment with convalescent blood products (z = 6.50; P < 0.001), and there was no statistical evidence of heterogeneity (Q = 2.76; I² = 0%; P = 0.43). The pooled estimate should be interpreted with caution and should not be generalized to other strains of virulent influenza without further study. Percentages have been rounded to the nearest whole integer. *The treatment day of a fatal case could not be determined and was excluded from analysis of early versus late treatment (19, 20).