The Centers for Disease Control and Prevention lists three types of influenza virus: Type A, Type B and Type C. Some types have subcategories. The CDC estimates that between 1976 and 2007 there have been upward of 49,000 deaths in the United States related to the influenza virus. The time between infection from the virus and the presentation of symptoms is called incubation. According to the University of South Carolina, this usually takes 18 hours to three days.
Type A
Type A virus may mutate while living in an avian host, such as a duck. The CDC states that this constant changing of the viral makeup over the flu season makes it difficult to find an antibiotic that is effective against all the different mutations. This accounts for the epidemics seen with influenza, especially those associated with the Type A virus. The CDC finds that 90 percent of deaths linked to influenza occur in the 65-plus age bracket.
Type B
Because Type B virus does not live in host animals, it is hypothesized that this is the cause of the few mutations seen with this particular type. The University of South Carolina explains that this means any antibiotic effective against the virus will probably remain effective for the length of the flu season, making it easier to control. The university does not say that Type B does not mutate, only that mutations are less likely. However, it adds that Type B influenza has been the cause of epidemics in some years.
Type C
Of the three types of influenza virus, Type C is considered the least worrisome and rarely, if ever, has an epidemic been charged to Type C. The CDC points out that the presenting symptomology with Type C is mild respiratory illness unlike the more severe signs of Types A and B. The CDC concludes that this may be the reason vaccination development is focused on the latter as opposed to the former virus.
