What Are the Ingredients of a Flu Shot?


Each year millions of people around the world receive the flu vaccine to prevent the onset of the influenza virus. But just what is contained inside the flu vaccine, and how does it work to prevent flu? This article explains what is contained in the different flu vaccine delivery methods, such as injection or nasal spray.

History and Evolutions

While influenza may be considered a nuisance or minor health problem by today's standards, in the early 20th century, according to the World Health Organization, strains of the Spanish Flu killed millions of people. Few treatments were available to definitively cure the flu, and researchers began looking for a method to prevent the flu virus. When researchers discovered the presence of viruses growing in chicken eggs, steps were taken to harness these viruses into a usable vaccine to prevent the flu. While the vaccine has undergone many re-toolings, the principle of using viruses found in chicken eggs is still in place today.

Virus Selection

The flu vaccine given each year is actually a combination of different viruses, the makeup of which varies annually. Each year, researchers and physician affiliates of the World Health Organization meet to discuss samples collected from flu viruses around the world. If strains that have the potential to start a pandemic (pervasive or worldwide form of flu), these are identified and selected to be included in the vaccine. While there are many steps to the process of creating a flu vaccine each year, the vaccine is basically selected, tested and purified numerous times to ensure the least amount of allergic reaction possible when given to humans. The viruses themselves to be included in the vaccine are grown in hen's eggs, because they are readily available and provide a good environment to grow the vaccine.


Once the vaccine has been manufactured and thoroughly tested, it is put into vaccine form. The flu shot itself includes inactivated viruses (grown within the eggs), formaldehyde for preservation and to kill the viruses and a preservative known as thimerosal that is present in only trace amounts, according to the CDC. Due to the fact that the vaccine is produced in chicken eggs, those that are allergic to poultry and poultry products should not get the vaccine for fear of adverse reaction.

Intra Nasal

When compared to the vaccine, the makeup of the nasal spray flu vaccine (brand name FluMist) does not contain thimerosal. The nasal spray also contains live, but very weak, viruses in low doses, compared with the deadened viruses contained in the shot.

Future Alternatives

Researchers are currently seeking out other options to manufacture flu vaccine ingredients, including the vaccine Optaflu, which uses a mammalian cell line (as compared to birds) to create the viruses for the vaccine. While Optaflu has not yet been approved in the United States, it is currently approved for use in the European Union countries. Optaflu shows particular promise because those who are allergic to birds and were previously not able to receive the shot could now get a flu shot.

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