Method for preserving viral particles

1. A method for preserving viral particles comprising:

(i) providing an aqueous solution of one or more sugars, a polyethyleneimine and said viral particles wherein, (a) the concentration of polyethyleneimine is less than 5 nM based on the number-average molar mass (M n ) of the polyethyleneimine, and (b) said aqueous solution comprises sucrose at a concentration of 0.8M or greater; and

(ii) freeze-drying the solution to form an amorphous solid matrix comprising said viral particles.

2. The method according to claim 1 , wherein the concentration of polyethyleneimine is between 0.0025 and 5 nM, based on the number-average molar mass (M n ) of the polyethyleneimine.

3. The method according to claim 1 , wherein the concentration of polyethyleneimine is between 0.025 and 2.5 nM, based on the number-average molar mass (M n ) of the polyethyleneimine.

4. The method according to claim 1 , in which the M n of the polyethyleneimine is between 20 and 1000 kDa and the concentration of the polyethyleneimine is between 0.001 and 5 nM based on the M n .

5. The method according to claim 1 , wherein the M n of the polyethyleneimine is between 300 and 2000 Da.

6. The method according to claim 1 , in which the sugar concentration, or total sugar concentration, is between 0.8M and 2M.

7. The method according to claim 1 , wherein said aqueous solution further comprises stachyose, raffinose or a sugar alcohol.

8. The method according to claim 1 , wherein said aqueous solution comprises one or more additional sugars.

9. The method according to claim 8 , wherein the concentration of sucrose relative to another sugar is at a ratio of between 3:7 and 9:1; and the concentration of polyethyleneimine based on M n in step (i) is between 0.0025 nM and 5 nM.

10. The method according to claim 1 , in which the viral particles are composed of a live virus or killed virus.

11. The method according to claim 10 , in which the live virus is whole virus or live-attenuated virus.

12. A method of preparing a composition comprising viral particles, which method comprises:

(a) providing an aqueous solution of one or more sugars, a polyethyleneimine and said viral particles, wherein (i) the concentration of polyethyleneimine is less than 5 nM based on the number-average molar mass (M n ) of the polyethyleneimine, and (ii) said aqueous solution comprises sucrose at a concentration of 0.8M or greater;

(b) adding an adjuvant, buffer, antibiotic and/or additive to the admixture; and

(c) freeze-drying the solution to form an amorphous solid matrix comprising said viral particles.

13. The method according to claim 12 , wherein said composition comprises two or more different types of viral particles.