Zanamivir (Acme Bioscience) was dissolved in Opti-MEM at a concentration of 50 mM and stored at −80°C. Monoclonal anti-HPIV3 HN antibodies were custom elicited in rats (Aldevron) using eGFP-HN complementary DNA, diluted in Dulbecco’s PBS (DPBS) to 100 μg/ml, and kept at 4°C. PIA174 antibody fragment (Fab) and full antibody (Ab) were purchased from Creative Biolabs. PA3/F4 was purified by Rockland Immunochemicals Inc. and was originally generated as described in (46 (link)).