It is the presence of antigens in the vaccines that helps build immunity against the disease-causing agent. Vaccines comprise suspending fluid, the inactivated or the live attenuated (weakened and less virulent) form of the disease-causing organism, and chemical additives (stabilizers, preservatives, and adjuvants). The chemicals are added to preserve the vaccine, and to ensure that it doesn't become less potent with time. In case of the flu shots, safety concerns were raised due to the presence of ingredients such as aluminum, mercury, and thimerosal. Let's find out more about these flu shot ingredients.
What Does the Flu Shot Contain?
Several influenza vaccines are marketed by different pharmaceutical companies. Here's some information on the components of these vaccines.
Strains of Influenza Viruses
These contain strains of two type A influenza viruses and a type B influenza virus that are chosen by the U.S. Centers for Disease Control (CDC) and the World Health Organization (WHO) every year. These are available as inactivated injectable vaccine and live attenuated vaccine. The former comes in single-dose vials and multi-dose vials, while the latter is inhaled through the nose.
Preservatives are added to prevent contamination. While the injectable ones that have the inactivated virus strains in multi-dose vials contain thimerosal, the live attenuated flu vaccines and the injectable ones that come in single-dose vials don't contain thimerosal. Thimerosal is a preservative which has been used in vaccines since 1930s. It contains about 49% ethylmercury. It is used in case of multi-dose vials as a new needle and syringe has to be inserted in each of these vials for drawing out each dose. This preservative is added as there's a risk of microbes being introduced as a needle is inserted.
Since exposure to mercury causes adverse effects, concerns were raised about the use of thimerosal. As a result, in July 1999, the American Academy of Pediatrics, and manufacturers of vaccines decided that they would discontinue the use of thimerosal or use it in minimal amounts. Though there have been allergic reactions such as redness and swelling at the injection site, there's a lack of evidence regarding the amount that can be used safely. An allergic reaction can be avoided by administering shots that don't contain this preservative.
Adjuvants and Stabilizers
Aluminum salts are used as adjuvants for stimulating a stronger immune response to antigens. The stabilizers include sugars and gelatin. These are used so that the vaccine doesn't lose its potency when it is stored or being transported.
The other ingredients include residual antibiotics and inactivating ingredients. For instance, antibiotics are added to prevent the growth of bacteria. Formaldehyde is added to kill viruses/bacteria and inactivate toxins. Vaccines that are prepared using chicken eggs would contain egg proteins.
According to the CDC, small amounts of thimerosal gives rise to minor reactions like redness and swelling at the injection site. Conclusive evidence is required to prove that this mercury-based preservative can cause serious harm. There have been moderate allergic reactions to influenza vaccine, wherein the affected child or adults experienced fever, local reactions, headache, fatigue, nausea, sore throat, stuffy nose, cough, muscle aches, and joint pain.
Since the vaccines are prepared in animal proteins, some people might develop an allergic reaction. People who have had a severe allergic reaction to egg, or those who have earlier had a severe allergic reaction to the shot must not get vaccinated. Guillain-Barré Syndrome (GBS), which is a neurological disorder that is characterized by temporary or permanent paralysis, has been linked to influenza vaccinations. Other complications that have been reported include Bell's palsy, shock, convulsions, breathing problems, etc.