So, just how does the flu jab work?

With issues regarding supply and demand for the influenza vaccine so much in the press over recent weeks, it is a useful time to examine current and future developments in influenza vaccine design.

When our body encounters an infectious agent, such as a bacteria or a virus, we produce cells to fight the infection and memory cells, that facilitate a quicker, more vigorous response if the agent is encountered a second time.

We can therefore develop immunity to a virus after either we have been infected by it or we are exposed to the virus through immunisation.

Influenza is an acute infection resulting from a virus that is easily transmitted from person to person.

There are two current treatment strategies: vaccination to prevent initial infection and treatment with antiviral drugs such as Tamiflu.

Unlike antibiotics, antiviral drugs do not destroy their target pathogen; instead they inhibit their development and specific antivirals are used for specific viruses.

The strains of virus responsible for the majority of infections can change year on year, thus necessitating changes in the formulation of the vaccine for the upcoming season.

Since it takes up to six months to create, manufacture, test, and prepare enough vaccine, scientists must decide in advance which strains they expect to dominate in the upcoming season.

The composition of virus vaccines for use in the 2010-2011 northern hemisphere influenza season recommended by the World Health Organization in February, 2010, comprises three strains: an A/California/7/2009 (H1N1)-like virus; an A/Perth/16/2009 (H3N2)-like virus and a B/Brisbane/60/2008-like virus.

The H1N1 strain used in this composition is the same strain used in the 2009 flu pandemic vaccine.

There are two main types of vaccines, live attenuated vaccines and inactivated vaccines.

Attenuated vaccines contain the infectious agent but they have been weakened, for example by heat or genetic modification. Thus, they tend to be more effective than those containing the inactivated agent and can shorten vaccine production times but are more susceptible to adverse reactions.

Adjuvants, or compounds, can be added to vaccines to stimulate the immune response.
Until recently, the only ones licensed for humans were based on aluminium or calcium salts.

New-generation adjuvants have been used to strengthen the response and thereby reduce the amount of antigenic material required to induce an effective immune reaction. In recent research reports adjuvanted H1N1 swine flu influenza vaccine achieved a stronger and more rapid response.

There is much research on new types of vaccines, such as DNA-based, and some have been developed and introduced commercially for other infections.

These vaccines tend to be safer and cause less reaction than older-style vaccines made from live or killed whole organisms but require the addition of adjuvants to improve their effectiveness.

Currently, influenza vaccines are typically given by injection into the muscle.

Influenza vaccines that could be administered by the respiratory or the oral route, or delivered through the skin without use of needles, are being developed as alternatives to traditional injected vaccines.

These may offer several advantages over intramuscular injections: they are pain- free, easier to distribute, and easier to give to patients, and their use could reduce vaccination costs.

They may also have advantages in terms of the type of immune response generated.

Several needle-free approaches to vaccination are at advanced stages of development and the days of the hypodermic needle in vaccination might be numbered.

Professor Conway is Professor of Pharmaceuticals, School of Applied Sciences, University of Huddersfield