The present invention provides a high growth reassortant influenza A virus having at least two gene segments of seasonal or pandemic strain origin, a PB1 gene segment of A/Texas/1/77 strain origin and a PA gene segment of A/Puerto Rico/8/34 (H1N1) origin coding for a PA protein comprising at least one amino acid modification at any one of positions 10, 275, 682, according to SEQ ID No. 1. Further provided are vaccine formulations comprising the reassortant influenza A virus of the invention.