As of November 2007 [update] , both the conventional injection and the nasal spray are manufactured using chicken eggs.  The European Union has also approved Optaflu , a vaccine produced by Novartis using vats of animal cells.  This technique is expected to be more scalable and avoid problems with eggs, such as allergic reactions and incompatibility with strains that affect avians like chickens.  Research continues into the idea of a "universal" influenza vaccine that would not require tailoring to a particular strain, but would be effective against a broad variety of influenza viruses. However, no vaccine candidates had been announced by Nov 2007. 
Children should be vaccinated every flu season for the best protection against flu. For children who will need two doses of flu vaccine, the first dose should be given as early in the season as possible. For other children, it is good practice to get them vaccinated by the end of October, if possible. However, getting vaccinated later can still be protective, as long as flu viruses are circulating. While seasonal influenza outbreaks can happen as early as October, most of the time influenza activity peaks between December and February. Since it takes about two weeks after vaccination for antibodies to develop in the body that protect against influenza virus infection, it is best that people get vaccinated so they are protected before influenza begins spreading in their community.