Is the flu shot safe?
The flu is a respiratory illness caused by the influenza virus. Symptoms of the flu are typically more severe than those of a cold. However, a vaccine is available that can keep the effects and risks of the flu at bay.
This common infection can also be life-threatening in some cases. According to the Centers for Disease Control and Prevention (CDC), hospitals admit 200,000 people each year for flu-related problems.
Young children, older adults, pregnant people, and individuals
with weak immune systems may be more likely to experience dangerous complications.
A flu shot contains weakened or inactivated flu viruses that bring the immune system into action without causing illness. These viruses instruct the immune system to make special proteins called antibodies.
The body stores antibodies and can use them to fight off a future flu infection. As a result, a person might be able to avoid the flu completely after receiving the shot, or only get a mild case.
Keeping an eye on hygiene and staying home when sick can help prevent the flu. However, most people should also get an annual flu shot.
This article explains the facts about how they work, their level of safety, any side effects.
Safety
The CDC states that flu shots have a long history of safe use.
The shot is recommended for people age 6 months and older, with only a few exceptions.
The following people should talk to their doctor before getting the shot:
those who are allergic to any ingredient in the flu shot or have had severe allergic reactions to the vaccine in the past
those who have had Guillain-Barré syndrome, a rare but severe paralyzing illness
people with a current illness, such as a fever
Egg allergies and the flu shot
Most flu shots contain a small amount of egg protein, and egg-free shots are available for those with severe egg allergies.
However, the American Academy of Allergy Asthma and Immunology (AAAAI), the American College of Allergy Asthma and Immunology (ACAAI), and the American Academy of Pediatrics (AAP) all agree that people with egg allergies can receive the flu shot without experiencing a severe reaction.
Pregnant women and the flu shot
The flu shot is safe and highly recommended for women during pregnancy.
It can be given anytime during pregnancy. Women who are pregnant may be more likely to have serious complications of the flu due to a higher strain on the heart, lungs, and immune system.
A study in the New England Journal of Medicine suggests that a mother might pass some of the protection of the flu shot on to her fetus. As infants cannot get the flu shot until they are 6 months old, this can help protect them during the interim period.
Effectiveness
The effectiveness of the flu shot can vary widely from year to year and depends on two main factors:
the health and age of the person getting the shot
how well the shot matches the flu strains active in that year
How health affects the flu shot
The flu shot seems to function better in adults and older children. People over the age of 65 years tend to have weaker immune systems, and the shot might be less effective for them.
Children under the age of 2 years and people with long-term health conditions might respond less to the shot and receive weaker protection. A person can receive the shot from the age of 6 months onward.
The CDC recommends yearly shots for children under the age of 2 years and over the age of 65 years, especially as they are most likely to experience serious complications from the flu.
Matching the shot to the strain
Every year, new strains of the flu spread around the globe. There are hundreds of different strains, but the manufacturers of influenza vaccines can only include 3 or 4 types in the shot each year.
Medical researchers must narrow it down to the strains that are most likely to make people sick. A few months before flu season arrives, researchers study the flu strains that were most common the year before.
They also examine strains that are spreading in other parts of the world. They use this data to predict which strains of flu will affect people during the upcoming flu season.
Sometimes, experts can accurately predict which strains of flu will spread, and the shot is considered a good "match." When this happens, the vaccine offers more protection for those who receive it.
The 2011 to 2012 flu shot was a good match, and a study in Clinical Infectious Diseases states that it was 71 percent effective that year.
However, in other years, the shot may be a poor match. This happens when flu predictions are inaccurate or the virus changes before flu season begins.
Even when the virus is a poor match, however, the shot may still be helpful. During the 2014-2015 flu season, for instance, one of the viruses mutated, leading to a less effective flu shot match. It was also considered to be a particularly severe flu season.
Despite these problems, the journal Open Forum Infectious Diseases reports that the shot was 41 percent effective for younger people, and 56 percent effective for people age 65 years and older.
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