To answer the original question -
"Ingredients
Several different brands of flu vaccine are used in the UK each flu season. For full information on ingredients, ask for the Patient Information Leaflet for the vaccine you are offered or look the brand name up on the electronic Medicines Compendium (eMC) .
Inactivated flu vaccines usually contain very small amounts of egg proteins (ovalbumin), as the virus is often grown on hens’ eggs. People who are allergic to eggs should ask their doctor for advice. With specialist medical advice, they may be able to receive a vaccine with a very low ovalbumin content or the cell-based quadrivalent vaccine as an alternative to those grown on eggs. See more information on egg proteins in vaccines at vk.ovg.ox.ac.uk/vk/vaccine-ingredients#egg%20proteins . Public Health England produce an information sheet showing the ovalbumin content of flu vaccines in the current flu season (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/996263/PHE_Influenza_vaccines_and_Ovalbumin_table_2021_to_2022.pdf )
Inactivated flu vaccines used in the UK often contain very small amounts of the following ingredients:
Sodium and potassium salts, used as acidity regulators
Polysorbate, used as an emulsifier (to hold other ingredients together)
Fluad, the vaccine recommended for people aged 65 and over, contains a small amount of an adjuvant called MF59. Adjuvants are substances which help to strengthen and lengthen the immune response to the vaccine. The main ingredient in MF59 is squalene oil, a naturally-occurring oil found in humans, plants and animals.
Flu vaccines may also contain tiny traces of these products used during the manufacturing process:
antibiotics (gentamicin, neomycin, kanamycin or polymyxin), used to stop bacteria growing and contaminating the vaccine
formaldehyde, an organic compound used to inactivate (kill) the viruses
From vk.ovg.ox.ac.uk/vk/inactivated-flu-vaccine