Johnson A, Chen LM, Winne E, Santana W, Metcalfe MG, Mateu-Petit G, Ridenour C, Hossain MJ, Villanueva J, Zaki SR, Williams TL, Cox NJ, Barr JR, Donis RO. Identification of Influenza A/PR/8/34 Donor Viruses Imparting High Hemagglutinin Yields to Candidate Vaccine Viruses in Eggs. PLoS One. 2015; 10(6):e0128982.