Too numerous. 60% effective predicted this year but variable with ingredients and what flu gets spread!!
Flu Vaccine Efficacy. The influenza virus has three categories A, B, and C. Influenza virus A and B cause seasonal epidemics during winter in the USA, not C. The CDC estimates that the flu vaccine confers around 50-60% protection when the flu viruses in the vaccine that are chosen match the major circulating epidemic strains, age and health factors also affect efficacy. http://www.cdc.gov/flu/about/qa/vaccineeffect.htm.
Hundreds of strains. Vaccine covers the prevalent stains over the past 2 years. Usually offer 70-80% coverage, Better than nothing.
A,B and C. There are three major Types of Infuenza.Type A&B cause annual Inflenza and C causes mild disease. TypeA can also infect animals and the virus is constantly changing in character and causes epidemics Type B Only infects humans and do not cause Pandemics like TyprA. Type C infects only humans and causes milder illness.
Flu. The vaccine is developed every year based on world trends and in general is very effective.