Antibodies were tested at 10 µg/ml and threefold serial dilutions until a nonbinding concentration was determined. Each antibody was tested in at least two (and typically more) replicates for specificity and affinity estimations. Note that only 14 of 15 HA-binding antibodies have curves in G because one of the HA-reactive antibodies only binds HA on whole virions, not on the recombinant protein.