Influenza evolves. Every year, every season, the flu is different. That’s why the flu vaccine has to change every season, and why a vaccine only lasts a year and needs to be readministered annually. Anyone can get the flu, but vaccination is particularly important for children between six months and two years old, adults over 65, and people with chronic illnesses. Pregnant women should also be sure to get vaccinated; not only is there no evidence that the flu vaccine will harm the baby, there is a strong association between the flu itself and fetal death. Only 47 percent of pregnant women get vaccinated, even though it’s much safer for the baby for them to do so than not. Flu season is peaking now, but it’s not to late to get protected.
Often, people don’t get vaccinated out of fear. Often, these fears are unfounded. For example, people are often afraid that if they get vaccinated too early, its effectiveness will wear off. In fact, it never wears off. The only reason you need to reup every year is to get protected against new strains; each season’s shot protects you against that season’s variety of flu for years to come. Indeed, the protection lasts longer than the strain does even if you get vaccinated early.
Another fear is that the vaccine will itself make you sick. While there are side effects in a small number of people, and there’s a two-week window after vaccination during which you are not yet fully protected, the vaccine itself does not cause flu. What does sometimes happen is the immune response to the viruses in the vaccine causes symptoms that appear similar to those of flu—but much weaker. However, this isn’t a sign of illness, and it doesn’t have the other health effects of flu, such as opportunistic bacterial infections and other potential damage.
People who have had a severe reaction to the vaccine in the past should talk to a doctor before getting vaccinated again. Similarly, most vaccines use ingredients derived from chicken eggs, and so people with egg allergies should likewise talk to a doctor. If you’ve had Guillain-Barré syndrome and you’re not in a high-risk group, let your doctor know before getting vaccinated. If you’re immunocompromised, that’s something else you should discuss. If you have an illness with fever, wait until you recover before getting the vaccine.