Abstract
Influenza is one of the most important respiratory infections of humans; it is responsible for an
estimated half million deaths worldwide each year. Recently, the influenza pandemic caused by a new
strain of influenza A (H1N1) 2009 virus was declared by the World Health Organization, whereby the
pandemic level has been raised from phase 5 to phase 6, as defined by a widespread human-to-human
transmission and sustained community level outbreaks in more than one region of the world. The guidelines
for prevention include routine recommendations on basic personal hygiene and annual vaccination,
which by far is considered the best possible method of prevention especially for high-risk populations.
Influenza vaccines, mostly trivalent, are indicated for the active immunization of individuals against seasonal
influenza caused by influenza viruses subtypes A and type B contained in the vaccine. However,
the protection is transient and yearly immunization is thus necessary. In addition, the antigenic changes,
i.e., antigenic drift and antigenic shift, in influenza viruses necessitate yearly surveillance for emergent
strains and incorporation of such strains into the current year’s vaccines. At present, two types of vaccines
are available, namely, inactivated (killed) vaccines administered by injection and cold adapted, liveattenuated
vaccine administered by nasal inhalation. This mini-review provides a brief description of
influenza vaccines with respect to their types, composition, method of manufacture, indication and usage;
a list of USFDA-approved commercial vaccines is also included.
