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Health Education

Does the flu shot make you tired?

Feeling wiped out after your vaccine is part of your body’s immune response
Heidi Borst
By | Sep. 10, 2024 Medically reviewed by Marissa Walsh, Pharm.D., BCPS-AQ ID
vaccination next to sleepy clouds - does the flu shot make you tired

Key takeaways

  • The flu shot can lead to mild side effects in some individuals, such as fatigue, fever, body aches, headache, and injection site reactions.

  • Tiredness from an influenza vaccination is a natural part of the immune response and usually lasts one to two days.

  • Staying well-hydrated and getting adequate rest can help lessen flu shot side effects. Relaxing your arm during the shot and moving it gently afterward can also minimize symptoms.

  • Annual flu vaccinations are crucial for preventing serious illnesses linked to the flu virus.

In this article:

An estimated 8% of Americans get the flu each year, according to the Centers for Disease Control and Prevention (CDC). If you’ve ever been suddenly sidelined by influenza, you’ve experienced the misery of being completely drained—too weak to even get out of bed. As you wait for the debilitating flu infection to run its course, you’d do anything to speed up the process.

Luckily, the flu shot is an effective way to prevent and decrease the risk of severe illness from the influenza virus, a pathogen known for causing significant respiratory illnesses during seasonal outbreaks. Administered annually (ideally before the flu season, which peaks from December to February in the United States), flu vaccines work by preparing the immune system to recognize and combat the flu effectively. Although not everyone will experience side effects like fatigue from flu shots, it is possible to feel icky and exhausted post-jab. Here’s what to know.

Does the flu shot make you tired?

Thanks to vaccines like the flu shot, millions of Americans stay healthy, says Jeffrey Zavala, MD, FAAFP, a family physician in Billings, Montana, and board member of the American Academy of Family Physicians (AAFP). “An annual seasonal flu vaccine is the best way to help reduce the risk of getting flu and any of its potentially serious complications,” he says.

Anyone older than six months of age should get an annual flu shot to prevent them from getting the flu—or make their symptoms less severe if they do catch it, according to the CDC.

In some cases, getting the flu shot can cause side effects. For example, tiredness or fatigue can be a side effect of the flu shot; however, it’s not very common, says Raj Dasgupta, MD, pulmonologist and program director with Huntington Health Hospital in California. Most influenza vaccine reactions are mild and resolve quickly. “Most people don’t have any reaction or side effects, but if you do feel tired, it’s usually mild and goes away in a day or two,” says Dr. Dasgupta.

RELATED: Flu symptoms 101

Why does the flu shot make you tired?

“Side effects happen because the vaccine is doing its job by activating the immune system,” says Dr. Zavala. After a flu shot, your immune system kicks into high gear, creating antibodies and activating immune cells to prepare for a potential influenza infection. While essential for building immunity, this process can leave you feeling somewhat drained.

In addition to fatigue, the most common side effects associated with the flu shot include:

  • Soreness, redness, and swelling at the injection site
  • Headache
  • Low-grade fever
  • Nausea
  • Muscle aches

 Allergic reactions are possible. In the past, concerns about those with egg allergies receiving certain formulations of the flu vaccine existed, but as of the 2023-2024 influenza season, the CDC has stated that additional precautions are no longer recommended; individuals with egg allergies may receive any vaccine otherwise indicated based on age and underlying conditions. However, if you experience the following potentially life-threatening signs of a severe allergic reaction for any reason, seek immediate medical attention:

  • Breathing problems like hoarseness or wheezing
  • Hives
  • Weakness
  • Dizziness
  • Paleness
  • Fast heartbeat

There is a small increased risk of Guillain-Barré syndrome associated with the influenza vaccine, occurring in about one or two cases per million people vaccinated.

RELATED: 10 common myths about the flu shot

How long does the flu shot make you tired?

“If you experience mild reactions like tiredness, they usually don’t last long—typically just a day or two,” says Dr. Dasgupta, adding that symptoms typically present within the first few days after vaccination. While the experience can vary from person to person, most people start feeling normal quickly after getting the flu shot.

 “The vaccine itself is cleared from your body within a few hours or days as your immune system processes it,” Dr. Dasgupta says. Mild reactions are common and indicate that your immune system is responding to the vaccine.

Dr. Dasgupta suggests ensuring you’re well-rested and hydrated before getting vaccinated to minimize or prevent side effects. Dr. Zavala recommends keeping your arm and shoulder relaxed during the shot and moving your arm regularly to help prevent stiffness and pain afterward. “It’s a good idea to choose a time when you won’t be doing a lot of activity, especially anything strenuous, to give the arm time to heal,” Dr. Zavala says.

If you experience post-vaccine pain or swelling, Dr. Zavala suggests ice or a cold compress. For discomfort, fever, or other mild side effects, you can try over-the-counter pain relievers like Tylenol (acetaminophen), Advil (ibuprofen), or Aleve (naproxen). However, consulting with a healthcare provider for tailored recommendations is always a good idea.

RELATED: Is it too late to get a flu shot?

The bottom line

While the flu shot may result in temporary feelings of tiredness due to your body’s immune response, this side effect is typically mild and short-lived. The significance of receiving an annual flu vaccination cannot be overstated, as it plays a vital role in preventing serious health complications related to influenza, protecting your health, and contributing to the well-being of the wider community.

“Even when flu vaccination doesn’t prevent infection completely, it can help reduce the severity and duration of illness and prevent serious complications, including hospitalization and death,” emphasizes Dr. Zavala. He says this is especially important for vulnerable patients like those with chronic medical conditions, older adults, and young children. If you have questions about the flu vaccine or have health conditions that may put you at higher risk for complications from the flu, your healthcare provider can be a great resource.

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