higher in vaccinated people than in those not receiving the swine flu vaccine. Dengvaxia, the only approved vaccine for Dengue fever, was found to increase the risk of hospitalization for Dengue fever by 1.58 times in children of 9 years or younger, resulting in the suspension of a mass vaccination program in the Philippines in 2017. Pandemrix a vaccine for the H1N1 pandemic of 2009 given to around 31 million people was found to have a higher level of adverse events than alternative vaccines resulting in legal action. In a response to the narcolepsy reports following immunization with Pandemrix, the CDC carried out a population-based study and found the FDA-approved 2009 H1N1 flu shots were not associated with an increased risk for the neurological disorder. Ingredients The ingredients of vaccines can vary greatly from one to the next and no two vaccines are the same. The CDC has compiled a list of vaccines and their ingredients that is readily accessible on their website. Aluminium Aluminium is an adjuvant ingredient in some vaccines. An adjuvant is a type of ingredient that is used to help the body's immune system create a stronger immune response after receiving the vaccination. Aluminium is in a salt form (the ionic version of an element) and is used in the following compounds: aluminium hydroxide, aluminium phosphate, and aluminium potassium sulfate. For a given element, the ion form has different properties from the elemental form. Although it is possible to have aluminium toxicity, aluminium salts have been used effectively and safely since the 1930s when they were first used with the diphtheria and tetanus vaccines. Although there is a small increase in the chance of having a local reaction to a vaccine with an aluminium salt (redness, soreness, and swelling), there is no increased risk of any serious reactions. Mercury Certain vaccines once contained a compound called thiomersal or thimerosal, which is an organic compound containing mercury. Organomercury is commonly found in two forms. The methylmercury cation (with one carbon atom) is found in mercury-contaminated fish and is the form that people might ingest in mercury-polluted areas (Minamata disease), whereas the ethylmercury cation (with two carbon atoms) is present in thimerosal, linked to thiosalicylate. Although both are organomercury compounds, they do not have the same chemical properties and interact with the human body differently. Ethylmercury is cleared from the body faster than methylmercury and is less likely