An influenza antigen is a piece of an influenza virus that is used to produce a flu vaccine. There are two types of pieces on the surface of the virus that serve as antigens, or agents, that induce antibody production. Antibodies are produced by the immune system to neutralize foreign substances in the body.
In the United States, influenza, or flu, is considered the seventh leading cause of death. It causes a lot of misery, lost work, and hospitalizations. Periodically, there are world-wide pandemics. These are outbreaks of new types of influenza, to which people lack resistance, that spread rapidly. Such outbreaks can kill tens of millions of people. This happened three times in the twentieth century.
To try and prevent contracting influenza, many people get a flu shot each year. These are actually inactivated material from virus particles that are introduced into the body by injection. The body’s immune system recognizes the influenza antigens as foreign, and makes antibodies against them. The immune system remembers that these antigens are foreign and will respond quickly to neutralize flu viruses that try to infect the person. The flu shot will only prevent infection if it has been made for the specific strain that is attacking the person.
The population of influenza viruses is constantly evolving. Thus, it is a prediction as to which strains of influenza will spread in the coming year. The vaccine is designed by the World Health Organization (WHO), and contains three different flu strains. One is influenza B, a less virulent type, and the other two are different strains of influenza A. It was strains of influenza A that were responsible for the 2009 swine flu and the 1918 Spanish flu pandemics.
The vaccines are made in chicken eggs using whole virus particles. The antibodies that give the boost to the immune system are made against two pieces of the virus that are found on its surface. Each influenza antigen is a protein. One is called hemagglutinin and binds the virus to the cell being infected. The other is neuraminidase, which is involved in processing sugars on the cell’s surface. This protein is a target for drugs that treat influenza.
Vaccines made with antigens to these particular influenza strains are effective against the viruses used to make the vaccine. They will, however, not be effective against viruses that have mutated and changed the structure of their antigens. There can be two types of changes in antigens. The influenza antigen can mutate and change its shape, or a new type of virus can form with mixed antigens from different types of virus. The latter is a more serious situation, since it often results in entirely new strains to which people have no resistance.
Antigen detection studies are used to identify outbreaks and decide if a person is infected with the influenza virus, and whether antiviral drugs should be used. Older tests utilized antibodies to the influenza antigen types to determine if the virus was present. These, while accurate, could be time-consuming. More recently, rapid influenza diagnostic tests (RIDTs) were developed that could give results within half an hour.
With fast-mutating diseases that spread easily, like influenza, it is always a race to try and stay ahead of the newest viral strain. The influenza virus lives in alternate hosts like birds, pigs, and even seals. It can suddenly mutate to spread to a new species. Even the standard seasonal flu kills a large number of people each year, and a pandemic of a highly virulent strain could pose a grave threat to human health.