What Are the Flu Shot Side Effects for the 2026-2027 Flu Season?

Q: Is it possible to get sick with the flu even if you have been vaccinated?

You may be exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with the flu before the vaccine begins to protect you. About two weeks after vaccination, antibodies that provide protection develop in the body. You may be exposed to a flu virus that is not included in the seasonal flu vaccine. Many different flu viruses circulate every year. The flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.

The flu vaccine can lessen the severity of illness in the very young and very old, along with those with conditions such as hypertension, diabetes and chronic respiratory illnesses. Since the flu vaccine can decrease the severity of the illness, particularly those who are medically vulnerable, the flu vaccine can lead to decreased hospitalization and mortality. Getting a flu shot is a personal decision and should be discussed with your doctor or healthcare provider.

Most people will not experience any side effects from the flu shot. But like any medical product, vaccines may cause some mild side effects that typically go away within a day or two.

What are common side effects from the flu shot?

Common side effects from the flu shot include:

Headache
Fatigue
Cough
Low fever
Arm soreness, redness or swelling lasting a couple of days

Is it possible to get sick with the flu even if you have been vaccinated?

Yes. You may have been exposed to a flu virus shortly before getting vaccinated or during the period that it takes the body to gain protection after getting vaccinated. This exposure may result in you becoming ill with the flu before the vaccine begins to protect you.

About two weeks after vaccination, antibodies that provide protection develop in the body.

You also may be exposed to a flu virus that is not included in the seasonal flu vaccine. Many different flu viruses circulate every year. The flu vaccine is made to protect against the three or four flu viruses that research suggests will be most common.

What are signs of an allergic reaction to the flu shot?

Fewer than 1 in a million people experience severe allergic reactions to the flu vaccine. If someone does have a severe allergic reaction, this would most likely happen within a few minutes of receiving the vaccine, which is why it is best to wait a few minutes at your doctor’s office after receiving any vaccine. Signs of an allergic reaction include:

Difficulty breathing
Hoarseness or wheezing
Swelling around the eyes or lips
Hives
Paleness
Weakness
A fast heartbeat or dizziness

If you believe you are having a severe allergic reaction and you are not at your doctor’s office, call 911 and get to the nearest hospital.

Can you get the flu vaccine if you are allergic to eggs?

People who have experienced only hives after exposure to egg can get any licensed flu vaccine that is otherwise appropriate for their age and health.

People who have symptoms other than hives after exposure to eggs, such as angioedema (swelling that may occur in the face, tongue, larynx, abdomen or arms and legs), respiratory distress, lightheadedness or recurrent emesis; or who have needed epinephrine or another emergency medical intervention, can also get any licensed flu vaccine that is otherwise appropriate for their age and health.

However, the vaccine should be given in a medical setting and be supervised by a health care provider who can recognize and manage severe allergic conditions. (Settings include hospitals, clinics, health departments and physician offices).