To investigate the physical and biological stability of PEG-modified liposome influenza vaccine lyophilized powder by influencing factor experiment and accelerated experiment and predict the validity period.

High temperature influencing factor test was carried out at (40±2) ℃, and accelerated test was carried out at 4 ℃ and (25±2) ℃. Physical stability was evaluated by appearance, particle size, encapsulation rate and stability coefficient. Spleen lymphocyte proliferation test and hemagglutination inhibition test were used to evaluate the biological stability, in which the stimulation index (SI) and antibody titer ratio (HI) were used as indexes. The validity period was calculated by using the classical constant temperature method and Arrhenius formula.

In the influencing factor experiment, the particle size and stability coefficient increased and the encapsulation rate decreased gradually after placing PEG2000 (3000/6000)-modified liposome influenza vaccine freeze-dried powder at (40±2) ℃ for 20 days. On the 10th day, the SI value of each PEG group was significantly bigger than that of the original solution group (P<0.05). The titer ratio of antibody before and after immunization was >4 for all PEG groups; on the 20th day, the SI value of each PEG group was significantly smaller than that of the original solution group (P<0.05); the antibody titer ratio of each PEG group after and before immunization was less than 4. In the accelerated experiment, three batches of PEG6000-modified liposome influenza vaccine lyophilized powder were placed at 4 ℃ and (25±2) ℃ for 3 months, the sample was stable at 4 ℃ with minor changing in particle size, encapsulation rate and stability coefficient, while at (25±2) ℃ the particle size and stability coefficient gradually increased, the encapsulation rate gradually decreased. There was significant difference in SI value between PEG6000 group and stock solution group under 4 ℃ storage condition (P<0.05), and no significant difference under (25±2) ℃ storage condition. For PEG6000 group, the ratio of antibody titer after and before immunization were ≥4 under both storage condition of 4 ℃ and (25±2) ℃. For the validity period prediction, the values of decomposition velocity constants K at 25 ℃, 30 ℃, 35 ℃ and 40 ℃ were 1.039×10^-3, 2.649×10^-3, 3.574×10^-3, and 4.868×10^-3 d^-1, respectively. The regression equation of lnK to 1/T was as following: lnK=20.195-8 148.5/T (r=0.917 9).

PEG-modified liposome influenza vaccine freeze-dried powder has good stability at (40±2) ℃ for 10 days, PEG6000-modified liposome influenza vaccine freeze-dried powder has good stability at 4 ℃ and (25±2) ℃ for 3 months. It is estimated that PEG6000-modified liposome influenza vaccine can be stored for 2.2 years, 3.3 months and 24 days at 4 ℃, 25 ℃ and 37 ℃ respectively.