Influenza vaccines are created by injecting a live virus into fertilized chicken eggs. The viruses are harvested, killed and purified, but a residual amount of egg white protein remains. Each year, vaccines are created to provide protection against the flu viruses expected to be prevalent in the upcoming cold weather months. For the 2017-2018 flu season, the vaccines are described as IIV3 and IIV4 for resistance to the expected three or four viruses. For adults ages 18 and older there is also an option to receive recombinant flu vaccines (RIV3 or RIV4) which are grown on mammalian cell cultures instead of in eggs, and so are no risk for people with severe egg allergy. Recommendations are that for people with a history of mild egg allergy should receive any IIV or RIV vaccine. People with a more severe allergic reaction may also receive any IIV or RIV, but in an inpatient or outpatient medical setting, administered by a healthcare provider. People with a known severe allergic reaction to influenza vaccine (which could be egg protein or the gelatin or the neomycin components of the vaccine) should not receive a flu vaccine.