Viruses are only able to grow in animal cells, so eggs or laboratory cell lines derived from animals play a necessary part in flu vaccine production.
Our standard quadrivalent vaccines are produced by processes that include culture in embryonated hens’ eggs. Only a trace of egg protein remains in the flu vaccine, but as the egg has been fertilised, some vegetarians and vegans may object to this.
Egg-free flu vaccines are produced in laboratory cell-based culture (based on canine kidney cells).
New recombinant vaccines are increasingly becoming available and are manufactured to a precise molecular formula; the process involves insect cells.
Vaccination is recommended because it provides the best protection against flu, a disease that can kill. The Vegetarian Society recommends that those at risk continue to accept medicines they need, including flu vaccination.
If you have religious reasons for avoiding eggs or any of the above technologies of the above, you should take appropriate religious advice.