Dueling articles on the flu vaccine shortage today in the Washington Post and NYTimes. The Times article is much better. As Russ Roberts, points out you have to wade far into the Post article before you get to a decent explanation of the shortage. The Times article correctly pinpoints low prices, liability and regulation early on (the same factors I wrote about here).
In recent decades, many drug companies in the United States abandoned the manufacture of vaccines, saying that they were expensive to make, underpriced and not profitable enough. Flu vaccine can be a particular gamble, because the demand for it varies from year to year and companies throw away what they do not sell because a new vaccine must be made each year to deal with changing strains of the virus. Some companies dropped out because of lawsuits, and others because they determined that it would not pay to retool aging vaccine plants to meet regulatory standards.