IFNA2 and susceptibility to pneumonia measurement: After adjustment for age and sex, patients with auto-Abs neutralizing high concentrations of both IFN-α2 and IFN-ω were found to have the highest risk of critical influenza pneumonia (OR = 139.9 in patients <70 yr old, OR = 11.7 for all ages), whereas patients with auto-Abs neutralizing low concentrations IFN-α presented a smaller increase in the risk of critical pneumonia (OR = 6.6 in patients <70 yr old, OR = 2.8 for all ages).