These predictions are based off of on-going research from the Center for Disease Control. The CDC receives samples of flu strains from around the world. They are tested and catalogued and compared to other strains to determine which are the most devastating and which have the greatest potential for widespread contamination. CDC fieldworkers also stay in touch with health and city officials to watch for any potential outbreaks and changes in the normal patterns for certain flu strains. For example, a strain that originated as a serious flu in Africa would be watched closely and as soon as any serious spread occurs, the CDC would be alerted and the strain would be high on the list for inclusion on that year’s flu vaccine.
All of these observations are recorded and recommendations are made at a meeting of the US Food and Drug Administration Vaccines and Related Biological Products Advisory Committee. It is then time to debate which strains have the most potential for spread, impact, and severity. Issues such as how each strain spreads, how they react to previous flu vaccines, how fast are the strains travelling out of their original infection areas, and which strains can be mass produced in the lab easiest to make enough vaccines to be effective? These are just some of the questions that must be answered before the three strains can be chosen and the vaccine can be made.
Once a final three have been selected then it is the yearly race to begin producing enough doses of the flu vaccine. The flu vaccine is still made the way it always has been. Each virus strain is incubated in chicken eggs where it is grown for about 90 days. Then the eggs are opened and the virus, which has matured fully, is extracted. The virus egg mix is then purified and the virus is partially killed while still maintaining the shape and make-up of the proteins and cellular make-up. The final dosage for each shot given has very little of the actual virus in it- as little as fifteen millionths of a gram for each of the three strains. This minuscule amount though is enough to give most people a good level of protection against those flu strains.
However, there are some downsides to the flu vaccine, mainly it only protects against those three strains. If an individual comes into contact with another strain, they will not have any protection. Also, if a flu virus mutates after the vaccine has been created, then that particular strain will no longer have antibodies built against it in people who received the shot. Additionally, some people cannot get the flu shot because they are allergic to the eggs the virus is grown in. Research is being done to try and develop an egg free way to grow the flu virus but as of yet no viable method has been found to mass produce the virus for vaccination purposes. Finally, some people do not tolerate the three strains in the shot and may become sick or develop symptoms and side effects to the shots- the flu, tenderness at the injection site, upset stomach, headaches, or other side effects.
In the end, it is a personal choice about whether one does or does not get the flu shot each year, but what is for certain is that a lot of work and research goes into making each new flu vaccines each year and a lot of work goes into trying to keep people healthy and safe from the flu.