Mutation of the Flu Cycle

Influenza is a virus that causes illness and sometimes can be fatal. There are two types that affect people and cause epidemics: influenza A and influenza B. Influenza C also affects humans but causes only mild illness and is not thought to be epidemic (cause mass infections).

Vaccines and Mutation

• Influenza mutates rapidly, and that is why flu vaccinations are updated yearly. The Centers for Disease Control (CDC) recommend getting a flu shot in September or later to combat the strains that are most common that year. Each year the vaccine protects against about three different flu types which make up the majority of flu infections that year. These vaccines will protect against the most common strains and reduce the risk of getting flu. The influenza A virus also infects birds and pigs, and human flu can borrow characteristics from animal viruses to create a new flu. This is what happened with the H1N1 "swine flu" virus, which is made up of human flu genes, pig flu genes and bird flu genes.

Immunity

• Flu viruses can mutate easily compared to some other viruses affecting humans. Small changes in virus DNA can allow the virus to alter enough so the human immune system can't recognize it and destroy the infection.

Seasonality

• Flu season runs through the winter in the Northern Hemisphere, when people are inside in colder weather. This allows the virus to easily jump from one person to another in an enclosed, unventilated space. January and February are peak months for flu in the U.S.