Flu season in the United States and Europe is approaching. Many people will roll up their sleeves for the jab. Some will be protected. Some will suffer. Sure, the numbers are pretty good — at best about 60 percent of people who get the shot will dodge the flu, at worst only 10 percent will be protected. The flu virus constantly mutates, which forces vaccine manufacturers to reformulate it every year. It takes about 7 months to make the vaccine so different strains pop up by the time it is ready which is the long standing explanation of why the vaccine often fails. But it’s more complicated than that. And something can be done about it. Why doesn’t the flu vaccine always work? Eggs The form of the virus used in the flu vaccine is actually grown inside of chicken eggs. Researchers discovered that mutations in the virus occur during this growth– often in regions important to triggering immune responses– and this can undermine the vaccine’s ability to protect people. Ferrets Ferrets are the most popular animal model for human influenza. The traditional way to select a strain for the vaccine involves injecting ferrets with an influenza virus used to make a vaccine strain, harvesting the antibodies, and then mixing them with a virus isolated from a human who recently had influenza. If the antibodies don’t stop the virus, the vaccine strain is changed. Aside from the fact that ferrets aren’t humans, antibodies aren’t viral sequences. Ghosts of flus past We repeatedly get flu vaccines and are naturally exposed to the virus in the wild. And it turns out that our first exposure in our lives oddly sets the table for all flu reactions after. This dizzyingly complex history makes predicting the impact of a flu vaccine in an individual staggeringly difficult. OK, so what can we do about it? Stop growing it in eggs and start using genetically engineered viral proteins Stop relying so heavily on ferrets and more purposefully factor in viral sequence data Learn more about the immune responses linked to protection and how to outwit the original exposure Incorporate parts of the virus that rarely mutate, ideally creating a “universal” shot that targets all strains and lasts for a lifetime But for now, experts say the flu vaccine, even given its limits, can still save lives and spare suffering for many people, especially anyone with a compromised immune system and the elderly.