There isn’t a single flu vaccine. The one you will receive will depend on your age and individual health.
There are different flu vaccines. They are either trivalent (containing three strains of the virus or quadrivalent (containing four strains) usually containing two influenza A viruses (like H1N1 and H3N2) and one or two influenza B viruses. The type you will receive will be dependent on a variety of factors of age, health, and current medical condition.
There are also different shots such as high dose ones, for those over 65 years old. A higher dose is needed for older individuals since they are less able to produce large quantities of antibodies on their own. The recombinant version is not made from eggs, unlike the more common versions. The last variety has an immune-boosting supplement called adjuvant, which helps those with less strong immune systems produce more antibodies.
