What Are The Side Effects of the H1N1 Flu Vaccine?

Medically Reviewed on 10/1/2021
H1N1, also known as the swine flu, most recently caused an outbreak in 2009. The vaccine for it used to be a separate shot, but is now included in your yearly flu shot. The side effects are similar to the flu shot, and are usually minor.
H1N1, also known as the swine flu, most recently caused an outbreak in 2009. The vaccine for it used to be a separate shot, but is now included in your yearly flu shot. The side effects are similar to the flu shot, and are usually minor.

H1N1 is an influenza virus also known as swine flu. In 1997, scientists confirmed this flu strain was the cause of the 1918 flu pandemic. The most recent outbreak of swine flu was in 2009.

Researchers were able to develop a vaccine to fight that strain of the virus. Now the flu shot you get every year includes protection against the H1N1 strain of the flu.

Side effects of the H1N1 flu vaccine

Throughout the 2009-2010 flu season, the CDC recommended that certain groups of people get the H1N1 flu vaccine, including:

  • People who were pregnant
  • People who were living with infants
  • Health care workers
  • People between the ages of 6 months and 24 years old
  • People between the ages of 25 and 64 years old who were immunocompromised
  • People who were in contact with someone who could not get vaccinated for medical reasons

Side effects of the vaccine given during the 2009-2010 flu season were similar to those from the regular annual flu shot. Side effects that may have occurred 1-2 days after receiving the shot included:

Other, more serious side effects like an allergic reaction would have occurred within a few minutes to a few hours after receiving the shot. Symptoms of a serious allergic reaction included:

Side effects of the influenza vaccine (flu shot)

Now, protection against the H1N1 strain of flu is included in the normal flu shot that many receive every year. Side effects of the flu shot are similar to those of the H1N1 flu vaccine and depend on which type of vaccine you receive.

Flu shot. Many people receive the flu vaccine as an injection in the arm. Side effects of this shot include:

  • Soreness, redness, or swelling at the injection site
  • Body aches
  • Low-grade headache
  • Fever
  • Feeling tired
  • Nausea

Some people faint after receiving injections like the flu shot. If you have a history of fainting or feeling dizzy after receiving a shot, let your doctor know before they administer the injection.

Nasal spray. Some people receive the flu vaccine as a spray through the nose. The side effects of this delivery method are different in children and adults. In adults, the side effects include:

In children, side effects include:

With any medication or vaccination, there is always a small chance of an allergic reaction. If you think you are having a severe allergic reaction to a medication or vaccine, call 911 or your country's emergency phone number right away. If you are having a minor allergic reaction, get in touch with your doctor as soon as possible.


Whooping Cough (Pertussis) Symptoms, Vaccine Facts See Slideshow

Other information about getting a flu shot

Who should not get it? Some people should not get the flu vaccine, including:

  • Babies less than 6 months old.
  • Anyone with an allergy to the flu vaccine or any ingredient in it. Many people with egg allergies need to take a specific flu vaccine that is egg-free.
  • Anyone who has been diagnosed with Guillain-Barré syndrome.
  • Anyone who is currently ill. You should wait until you are feeling better before getting the vaccine.

You can't get the flu from the flu vaccine. Today's version of the flu shot contains only dead viral material. It’s inactive, so you can’t get the flu from the shot. The side effects you may get from the vaccine are due to your immune system's response to receiving a vaccination.

The nasal spray does contain the live flu virus. However, it’s been altered so you can’t become infected with the flu from receiving the nasal spray.

It’s safe for pregnant people. The flu vaccine has been proven safe and effective for pregnant people. However, pregnant people should make sure to get the flu shot and not the nasal spray.

Pregnant people are more prone to complications if they get sick with the flu. Becoming infected with the flu while pregnant can also cause harm to the baby. Getting the flu shot helps to prevent you from getting the flu while pregnant. It also causes you to pass flu antibodies on to your baby, giving them protection once they are born.

The side effects of the flu shot are the same for pregnant people as they are for anyone else.

Vaccine safety. Both the CDC and the FDA monitor vaccine safety in the U.S. They use the following two systems: Vaccine Adverse Event Reporting System (VAERS) and Vaccine Safety Datalink (VSD).

Anyone can report vaccine side effects to VAERS online. Because of this, it’s hard to determine if the person's reaction or symptoms were in fact caused by a vaccine. However, this system helps the CDC and FDA look for patterns of reactions or symptoms in the general public.

VSD uses electronic health information from 9 different health care organizations across the country. It allows the CDC and FDA to monitor specific vaccine information as it relates to urgent care, hospital, and doctor's office visits.

Medically Reviewed on 10/1/2021
Centers for Disease Control and Prevention: "Flu Vaccine Safety and Pregnancy," "Flu Vaccine Safety Information," "General Questions and Answers on 2009 H1N1 Influenza Vaccine Safety," "Key Facts About Seasonal Flu Vaccine," "The Deadliest Flu: The Complete Story of the Discovery and Reconstruction of the 1918 Pandemic Virus," "Vaccine against 2009 H1N1 Influenza Virus," "Vaccine Safety Datalink (VSD)."

Mayo Clinic: "H1N1 flu (swine flu)."