Flublok does not require flu virus or eggs for manufacture
Historically, manufacturers have produced vaccine by growing the virus in eggs and then modifying it. This is effective but requires millions of fertilised eggs each year. This also means the vaccine can be unsuitable for people with egg allergies.
Growing the virus in cell lines is an alternative and, unlike eggs, cells can be frozen for later use, raising the possibility of responding to emergencies more rapidly.
In November 2012, the FDA approved Flucelvax from Novartis: the first vaccine based on cell lines, rather than eggs, to reach the market. Flublok is different in that its manufacture does not require flu viruses. It contains three, full-length, recombinant haemagglutinin proteins to help protect against two influenza virus A strains, H1N1 and H3N2, and one influenza virus B strain.