Recent problems have arisen due to the lack of flu shots available. In the past, there have been many different companies that make flu vaccines for the United States and other parts of the world. There were 25 makers in the 70's and now there are only 2. One of the largest factories of the flu vaccine is located in England and they have been shut down by the British regulators. That factory accounted for 46 million doses of flu vaccine for the United States. Also the flu vaccine that is given is not always dependable because there are hundreds of different types of diseases that can occur and the companies guess only one.
Another problem is how they manufacture the flu vaccine that they will use in the United States. They use a 30 year old system of using chicken eggs to yield a seed vaccine. Then after many months they can make it into a shot. Drug companies and many researchers believe they can update the system with using reverse genetics and then incubating the virus in humans and monkey cells. This will be more effective than eggs. I believe this is important because the flu virus kills an average of 36,000 American and hospitalizes another 114,000 per year.