You see, the flu vaccine as we know it is in a state of flux. No longer do you have to settle for a shot that only contains three strains of influenza, the virus that causes the flu. This year there are two vaccines—FluMist Quadrivalent (MedImmune) and Fluarix Quadrivalent (GlaxoSmithKline)—that contain four strains. The thought is that adding a strain will increase the protection against the ever-changing virus, says Pedro A. Piedra, MD, professor in the department of molecular virology and microbiology at Baylor College of Medicine.  And that isn’t the only choice you can make. Vaccines are either inactivated or live. Everyone 6 months of age and older can take the inactive vaccine (aka the flu shot), which means that you are not getting any live virus. According to the CDC, the inactivated flu vaccines contain a small amount of a mercury-based preservative called thimerosal. They’re delivered via needle and are of the three-strain variety, unless you ask for Fluarix Quadrivalent. The Live Attenuated Influenza Vaccine (LAIV) is good for healthy individuals between 2 and 49 years old and, since it is delivered via nasal spray, anyone who is needle adverse,  according to Dr. Piedra, who was involved in LAIV clinical trials phases I through IV. It contains a weakened virus but does not cause the flu. This year the nasal spray, also known as FluMist, will be the four-strain vaccine.  More from Prevention: Do You Have A Cold…Or The Flu?  And if you’re allergic to eggs, now there is a vaccine for you—FluBlok. Instead of harvesting the influenza virus in chicken eggs, the proteins of three flu strains that make up the FluBlok vaccine have been harvested in caterpillar eggs. Your choices aren’t only what kind of vaccine you receive, but also when you get it. “You get the most protection from an influenza vaccine when an individual has had time to develop a protective immune response and before the onset of the influenza season,” says Dr. Piedra. It takes about two weeks for the vaccine to prepare your immune system to fight any invading virus, so when the shot is available get it.  “The onset of the influenza season is unpredictable and can begin as early as October,” he says. Which is what occurred last year and peaked in the first or second week of January. And while the efficacy of the vaccine is dependent on the strains of influenza that circulate, there might be something you can do to stimulate your immune response to the vaccine—exercise. Recent research in Medicine & Science in Sports & Exercise found that moderate aerobic exercise after vaccination may help women between the ages of 55 and 75 years of age increase the vaccine’s stimulatory effect on the immune system against some strains of influenza. And other research found that aerobic exercise helped the flu vaccine’s efficacy in younger subjects, too. Either way, a brisk walk may help strengthen your immune system. This year, exercise your right to choose your flu protection. It’s nice to finally have a choice. More from Prevention: Best and Worst Natural Cold And Flu Remedies