Other methods of manufacture
Methods of vaccine generation that bypass the need for eggs include the construction of influenza virus-like particles (VLP). VLP resemble viruses, but there is no need for inactivation, as they do not include viral coding elements, but merely present antigens in a similar manner to a virion. Some methods of producing VLP include cultures of Spodoptera frugiperda Sf9 insect cells and plant-based vaccine production (e.g., production in Nicotiana benthamiana). There is evidence that some VLPs elicit antibodies that recognize a broader panel of antigenically distinct viral isolates compared to other vaccines in the hemagglutination-inhibition assay (HIA).A gene-based DNA vaccine, used to prime the immune system after boosting with an inactivated H5N1 vaccine, underwent clinical trials in 2011.On November 20, 2012, Novartis received FDA approval for the first cell-culture vaccine. In 2013, the recombinant influenza vaccine, Flublok, was approved for use in the United States.On September 17, 2020, the Committee for Medicinal Products for Human Use (CHMP) of the European Medicines Agency (EMA) adopted a positive opinion, recommending the granting of a marketing authorization for Supemtek, a quadrivalent influenza vaccine (recombinant, prepared in cell culture). The applicant for this medicinal product is Sanofi Pasteur. Supemtek was approved for medical use in the European Union in November 2020.Australia authorised its first and cell-based vaccine in March 2021, based on an "eternal cell line" of a dog kidney. Because of the way it is produced, it produces better-matched vaccine (to the flu strains).
Infection with influenza virus itself increases both the risk of death (up to one in ten thousand) and the risk of developing Guillain–Barré syndrome to a far higher level than the highest level of suspected vaccine involvement (approximately ten times higher by 2009 estimates).Although one review gives an incidence of about one case of Guillain–Barré per million vaccinations, a large study in China, covering close to a hundred million doses of vaccine against the 2009 H1N1 "swine" flu found only eleven cases of Guillain–Barré syndrome, (0.1 per million doses) total incidence in persons vaccinated, actually lower than the normal rate of the disease in China, and no other notable side effects. Egg allergy
Although most influenza vaccines are produced using egg-based techniques, influenza vaccines are nonetheless still recommended for people with egg allergies, even if severe. Studies examining the safety of influenza vaccines in people with severe egg allergies found that anaphylaxis was very rare, occurring in 1.3 cases per million doses given.Monitoring for symptoms from vaccination is recommended in those with more severe symptoms. A study of nearly 800 children with egg allergy, including over 250 with previous anaphylactic reactions, had zero systemic allergic reactions when given the live attenuated flu vaccine.