Getting a shot at the doctor's office might not be the most enjoyable experience—with the needle and the doctor and that pesky arm pain that can come after for some—but vaccination is necessary to help your body defend itself against dangerous diseases, including seasonal influenza (flu). There's a reason CDC recommends everyone 6 months of age and older get a flu shot each year: Anyone can get the flu and it can hit hard. The 2017-2018 flu season particularly demonstrated the impact: Around 80,000 Americans lost their lives due to influenza and 900,000 people were hospitalized.
The flu shot is safe, and you cannot get the flu from the flu shot. Most people have little or no reaction to the flu shot and the most common side effect is some discomfort in your arm hours after receiving the vaccination, including soreness, redness and/or swelling. A sore arm is much better than catching the actual influenza virus—which can knock you out for days or weeks with high fever, cough and muscle aches—but why do some people experience this particular side effect of the flu shot?
What are antigens?
When you receive a flu vaccination, your body is being introduced to antigens. Our bodies begin producing antibodies that provide protection against the virus strains in the vaccine. The influenza vaccine contains an inactivated virus, which is a "dead" virus designed to look like the actual influenza virus. Even though these viruses cannot make you sick, your immune system detects the virus as a threat and begins to fight it. "The reason why your arm specifically is sore is that your immune system is giving you a robust response to the flu vaccination," says Dr. Juanita Mora, American Lung Association volunteer spokesperson and allergist/immunologist.
How can I alleviate my arm pain?
Swelling, redness and soreness are common after the flu shot and can last 24-48 hours. "If you always experience soreness or swelling after a flu vaccination, take an ibuprofen about 2 hours prior to vaccination," suggests Dr. Mora. "You can also try icing the injection site to reduce redness and swelling and taking another dose of ibuprofen to ease any soreness or swelling."
What arm should I get my flu shot in?
Dr. Mora recommends getting the flu shot in the arm you use the least. "That way if you are writing or doing day-to-day activities, you're not aggravating the muscle even more," she says.
Some other ways to reduce pain include trying not to tense your arm while you're being vaccinated and moving your arm after vaccination (or exercising) to increase blood flow and help disperse the vaccine throughout the area.
What serious side effects mean I should call my doctor?
The flu vaccine will not give you the flu. However, some people do experience side effects. While redness, swelling, muscle aches and sometimes low-grade fevers (temperatures under 101 degrees F) are typical side effects after receiving an influenza vaccination, there can be some rare and serious side effects including difficulty breathing and swelling around the eyes or lips. If you are experiencing dizziness, a racing heart or a high fever (greater than 101) seek medical attention right away.
"If you develop full body hives, you are having an allergic reaction to the vaccine," says Dr. Mora. The most common allergic reaction is found in people allergic to eggs. This is because egg proteins are one of the products in the flu vaccine. However, if you have an egg allergy, you can still get the flu shot. Talk to your doctor about the best way to get vaccinated.
Why a little bit of arm pain is necessary each year.
Even if you received a flu shot in a previous year, you should still protect yourself with a new vaccination this year. This is because the vaccine is developed based on the specific flu strains scientists expect to be the most dangerous this year. Doctors recommend getting vaccinated in fall, but it is never too late to get the flu shot. Getting it late is better than not at all.
Blog last updated: November 30, 2021