Effect of stabilizing excipient combinations on HA activity after drying influenza vaccine on PDMS chips and storing with desiccant for up to six months at 40°C. Vaccine (B/Brisbane/60/2008) was formulated with two, three or four stabilizing excipients at a total stabilizer concentration of 10% w/v in ammonium acetate buffer. For the two-stabilizer combinations, the concentration ratio is shown, where the first number corresponds to the first excipient listed below it on the x axis. The combinations of three or four stabilizers all contained equal amounts of each excipient. T = trehalose, S = sucrose, A = arginine, H = sodium heptagluconate. Asterisk (*) indicates HA activity significantly decreased from HA activity on day 0 (Student’s t-test, p < 0.05). HA activity is shown as a percentage of concentrated stock vaccine solution. Data represent averages of n = 12 replicates, with standard deviation bars shown.