I cite as reference the front page story from the Denver Post, dated
Sunday, Dec 14 (you can check its website for the details). Briefly,
the article explains 2 issues involved with the current flu problems.

But before we launch into this, a short explanation how the
vaccine is produced. By Federal law, it can only be manufactured
using chicken eggs to ensure consistency and avoid impurities or
contamination. More on this later.

First, there are only 2 vaccine manufacturers left in the USA and they
produce vaccine in quantities defined by health professionals plus about
a 20% reserve. Last year 40 M doses were produced, we had a relativelys
mild flu season and 8M doses were destroyed. The past 3 years have
been moderately mild, so production was lower than ususal.

Second, at the time of the "definition" or composition of the vaccine
(which must be signed off by the FDA) there was concern about the
Fujian strain. In fact you might even go so far as to say there was
major concern by some members of the panel. However, at the time,
there was no way to get a sample of the virus from a human source.
It had been detected in canine livers (which, according to the article,
is a common way to detect and analyze). The opinion was that taking
the virus from the canine and incubating and producing within the
chicken eggs might have included other contaminants. Only after
the vaccine forumula was approved and produce began that the Japanese
were able to isolate a human sample.

Go read the entire article. Fascinating!