“Vaccination is the most effective way to prevent infection and severe outcomes caused by influenza viruses.” 1

“Influenza viruses undergo frequent changes in their surface antigens. Immunity resulting from infection by one influenza virus does not protect fully against antigenic or genetic variants of the same subtype (influenza A viruses) or type (influenza B viruses). As a consequence, influenza outbreaks occur every year. New influenza vaccines must be designed annually to match the circulating viruses which are expected to cause the next epidemic.” 2 Many groups world-wide are working on a universal flu vaccine that doesn't require changing each year. 3

There are two types of influenza vaccine. 4 The first is the inactivated vaccine which contains killed virus that is given with a needle, usually in the arm. The second type is the live, attenuated intranasal influenza vaccine (LAIV) that is given as a nasal spray (and can be used in people 2-49 years of age who do not have underlying health issues that predisposes them to influenza complications, and who are not pregnant). It takes about 2 weeks after vaccination for the antibodies that provide protection against the influenza viruses to develop in the body.

The effectiveness of flu vaccines in the real world are uniquely difficult as vaccines may be imperfectly matched, virus prevalence varies widely between years, and influenza is often confused with other influenza-like illnesses. However, in most years the flu vaccine strains have been a good match for the circulating strains and even a mis-matched vaccine can often provide cross protection. Flu vaccination, even with moderate effectiveness of about 60%, can also reduce the following: flu-related illness, antibiotic use, time lost from work, hospitalizations, and deaths. 5  Over the last 50 years, seasonal flu vaccines have had very good safety track records. 6

Development and production of influenza vaccines, planning for their supplies and use as well as provision of other respective health care resources are essential components of a comprehensive seasonal and pandemic influenza response. 2

1. WHO Influenza Vaccines
2. WHO Influenza vaccines: Position paper. Weekly Epidemiological Record, NO. 33, 19 Aug 2005
3. Du, Lanying; Zhou, Yusen; Jiang, Shibo Research and development of universal influenza vaccines. Microbes and Infection 2010,12 (4): 280–6.
4. WHO Biologicals: Influenza vaccines
5. CDC Vaccine Effectiveness for 2014-2015.
6. CDC Influenza vaccine safety