How do vaccines work?
Avian flu viruses, along with other viruses and bacteria foreign to the body, are classified as antigens. An antigen is defined as "a foreign substance that causes the immune system to make a specific immune response". An immune response to an avian flu virus antigen involves the making of antibodies, proteins that are specifically made to combat the type of virus.
Specifically, antibodies attack the avian flu virus by binding to its hemagglutinin surface proteins, rendering the surface proteins useless. This does two things: Since the avian flu virus uses hemagglutinin surface proteins to attach to and enter host cells, the virus is not able to infect more cells and reproduce, because it cannot use its surface proteins. Also, when antibodies are attached to the avian flu virus, they attract other cells which destroy the virus.
If the same type of virus infects the body a second time, there will be a much quicker and more powerful immune response. Since the body can already recognize the virus, antibodies immediately attack the virus, which stops it from causing disease. In this way, antibodies create “immunity” to diseases.
How vaccines help
The initial creating of antibodies takes a long time, so by the time antibodies are produced in an actual H5N1 infection, the body would be already damaged from avian flu, and it could be too late. An avian flu vaccine would give the body a chance to develop antibodies before an actual infection.
Vaccines work by artificially triggering an immune response to a certain antigen, without actually causing disease. There are many ways to do this, but the most common way for is to give a patient deactivated viruses (deactivated by taking the harmful genes out). The immune system responds to the inactivated viruses in vaccines in the same way it would respond to actual viruses, causing antibodies to be made. The body does not get sick from the disease because the viruses are deactivated.
After vaccination, if the body is attacked by the same type virus in the vaccine, the body will already have “immunity” to the virus because it already has the proper antibodies to fight the virus.