Technology Review Flu Vaccine Production: a "step through" of a brief article on what's required to make flu vaccine.
If you want, you can download a .pdf that really gives you a better picture of how things fit together, but the .pdf is 2.2 MB (it's 2 pages, but MIT uses great graphics) so it took quite a while on my connection.
The gist of it is, if you want to make a flu vaccine:
1. You buy 90 million (9*10^7) fertilized chicken eggs 6 months in advance for each strain of influenza that may need a vaccine. Usually that's been 3 strains in recent years, but you might be asked to do four.
2. You wait for the World Health Organization to guess what strain(s) of influenza will be popular this year.
3. You use samples provided by WHO of the 3 (or sometimes 4) strains that they're "betting on" to infect your eggs with both the influenza strain and a "harmless" carrier virus (remember 90,000,000 eggs per strain).
4. You incubate the eggs long enough for the viral payload to multiply.
5. You extract the viral material from all of the eggs - or course keeping the material from each egg separate, because the next step is to:
6. Sort through all the viral material obtained and find the samples that contain both the correct influenza viral signature and the right carrier viral material. (Enormous crap shoot here - with extremely variable yields)
7. Chemically inactivate all the "good samples" and package it up for distribution.
8. Chemically inactivate all the "not good samples" and put them in a hole somewhere.
8. Wait for the lawsuits to start.
If, as happened this year, you run into a glitch anywhere in the process, you chemically inactivate all the viral material from all of the eggs, and then you dig a very large hole and put 90 million (or 3 or 4 times 90 million) eggs in it and cover it up. Since it takes several months to get through the whole process, there is no way to recover within any single flu season.
Anybody want to go into this business?
The article linked describes an alternate method for replicating the sample viruses that WHO provides, that would eliminate the "crap shoot" over which are the good eggs and which are the useless ones; but it's at least 5 years from being proved safe, and being accepted by the international regulatory agencies, and thus far has been "demonstrated" only for small quantity production.