Flu vaccine protects against influenza infection and can also prevent complications such as dehydration, pneumonia, and worsening of existing health problems like asthma or diabetes. It’s recommended that everybody get the flu vaccine starting at six months of age. It is the single best way to prevent flu infection in any person. So even if a person has never had the flu before, you can’t predict that they’re not going to get the flu this time around. It’s important to get the flu vaccine every year because flu can cause severe illness even in healthy individuals. It’s especially dangerous for people with other conditions such as asthma or diabetes who can have complications if they do get the flu. There are two reasons why people need to get a flu vaccine every year. The first is that vaccine immunity can wane over time, and for the best protection, it’s important to get a flu vaccine every season. The second is that the strains of virus that circulate in a community are different from year to year, and so the vaccine formulation may change. A flu vaccine cannot cause a person to become sick. That’s because it’s made of either a killed virus or a weakened live virus. Although any vaccine can cause certain reactions or side effects, they cannot cause the flu infection itself. As with any injection, there can be a local reaction to the flu shot such as pain, redness, or swelling. There may also be body aches or mild fever. Brief fainting spells can occur after any medical procedure including vaccines, but the flu vaccine cannot cause flu infection.