The flu vaccine is an example of modern vaccination. Due to the change in [[allele]] frequency over time in the population of the influenza virus, new influenza vaccines are created each year. In some years the vaccines are less effective than in other years. According to the CDC,"Influenza viruses are always changing. Therefore, influenza vaccines are updated every year, and annual vaccination is recommended".<ref> "Inactivated Influenza Vaccine, What you need to know," a publication of the Center for Disease Control, 2006. Available online at: https://www.cdc.gov/nip/publications/VIS/vis-flu.pdf</ref> | The flu vaccine is an example of modern vaccination. Due to the change in [[allele]] frequency over time in the population of the influenza virus, new influenza vaccines are created each year. In some years the vaccines are less effective than in other years. According to the CDC,"Influenza viruses are always changing. Therefore, influenza vaccines are updated every year, and annual vaccination is recommended".<ref> "Inactivated Influenza Vaccine, What you need to know," a publication of the Center for Disease Control, 2006. Available online at: https://www.cdc.gov/nip/publications/VIS/vis-flu.pdf</ref> |