Can The Flu Shot Make You Sick?

By Michael Kopf, MD
Medically reviewed checkmarkMedically reviewed
April 7, 2022

Getting the flu is always an unpleasant experience. It can lead you to miss days from work, cancel plans with friends, and just be fairly miserable in general. 

Fortunately, every year there is a flu shot available to protect you from the strains circulating during the season.

One shot  can help prevent you from getting the flu and give you immunity throughout the flu season.

What is the Flu?

Commonly known as the flu, the influenza virus is a contagious respiratory illness that infects the throat, nose, and lungs.

There are two main strains of influenza, type A and B, that routinely spread and can cause seasonal flu epidemics each year.

Unfortunately, the flu is contagious and can become severe in the elderly, young children, and people with certain health conditions.

These demographics are at greater risk of serious flu complications.  


Common symptoms associated with the flu include:

In some cases, you may experience vomiting and diarrhea.

This tends to be more common in children than adults.

In other cases, you may experience many of the above symptoms but not necessarily a fever.

Flu symptoms can be severe.

If you have any of the following symptoms, contact your doctor immediately:


What starts off as a harmless sneeze or cough from someone close to you can lead you to become infected with influenza viruses that attack the nose, throat, and lungs.

Highly contagious, these viruses spread through droplets released into the air and even potentially into the mouths of others in close contact. 

You can also get the flu by touching a surface or object that was recently touched by an infected person if you then touch your own mouth, eyes, or nose.

The flu transfers easily, often spreading from one person to the next before they know they are even sick.

Once infected, you can develop symptoms as early as a day after contact and can be contagious beyond five to seven days after becoming sick.

Some people, especially young children and people with weakened immune systems, can be contagious for even longer. 

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What is the Flu Shot?

Influenza (flu) vaccines protect against the four influenza viruses that research indicates are the most common variants during the upcoming season.

Most flu vaccines are administered using a needle injected into the arm. There is also a nasal spray flu vaccine typically given to children.

Can the Flu Shot Give You The Flu?

The flu vaccine cannot give you the flu.

The CDC explains that the vaccine is made from inactive (dead) flu viruses that aren’t infectious, or with one gene from a flu virus, and not the whole virus, making it not strong enough to cause an infection.

It also does not protect you against COVID-19 or put you at a higher risk of getting COVID-19. 

According to the NHS, if you get both the flu and COVID-19 at the same time, you can become seriously ill.

Getting a flu shot along with the COVID-19 vaccine can provide you with protection from getting severely sick.

However, you may feel achy after the flu shot, specifically feeling sore at the injection site.

The vaccine is designed to protect you from getting the flu.

Common Side Effects

While the flu shot can protect you from getting the flu, you may experience side effects when the shot is given. These side effects tend to be mild and go away after a few days.

Common side effects from a flu shot include:

  • soreness
  • redness
  • swelling at the injection site 
  • fever
  • nausea
  • muscle aches
  • headache
  • fatigue

In some people, the flu shot can cause fainting. If you have fainted from receiving a vaccine before, let your healthcare provider know before they administer your injection.

Possible side effects from the nasal spray vaccine that can be experienced by children include:

  • runny nose 
  • wheezing 
  • headache
  • muscle aches 
  • vomiting 
  • fever, typically low grade 

Adults can have the following side effects from the nasal spray vaccine:

  • runny nose 
  • headache 
  • sore throat 
  • cough

Allergic Reaction

While rare, a life-threatening allergic reaction to flu shots can occur.

If you exhibit any of the following symptoms, you may be having an allergic reaction:

  • difficulty breathing
  • hoarseness or wheezing
  • hives
  • paleness
  • weakness
  • a rapid heartbeat
  • dizziness

These symptoms are typically experienced within a few minutes to a few hours after receiving the shot and among persons who are allergic to specific ingredients in the vaccine.

This could be reactions to egg protein or other ingredients.

The best way to avoid an allergic reaction is to inform your healthcare provider if you have had any previous allergic reactions to the influenza vaccine.

In rare cases, you may have an allergic reaction to the nasal spray vaccine.

The onset usually comes within a few minutes or a few hours.

Side effects of an allergic reaction include a ringing in your ears, vision changes, or feeling dizzy. Let your doctor know your symptoms immediately. 

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When to See a Doctor 

In most cases, you can overcome the flu with at-home treatments by getting plenty of rest, keeping up your fluids, and taking over-the-counter medications such as ibuprofen to manage your pain, and antihistamines to help with congestion.

Your symptoms should pass after about a week. However, you should seek medical advice if you have a fever that won’t break after taking fever-reducing medications.

In certain cases, the flu can turn severe.

Visit your doctor if you experience any of the following symptoms.

  • difficulty breathing 
  • shortness of breath
  • severe vomiting
  • chest or stomach pain
  • dizziness or lightheadedness
  • confusion

How K Health Can Help

Did you know you can get affordable primary care with the K Health app? Download K Health to check your symptoms, explore conditions and treatments, and if needed text with a provider in minutes. K Health’s AI-powered app is based on 20 years of clinical data.

Frequently Asked Questions

Can you get the flu from receiving a flu shot?
No, the flu shot cannot give you the flu. It is designed to protect you from the strains of influenza circulating that season.
How long do flu shot side effects last?
Side effects from the vaccine generally go away after a few days and tend to be mild. Contact your doctor if symptoms persist.
Are you contagious after a flu shot?
No, the flu shot cannot give you the flu or make you contagious. You may experience side effects after getting your vaccine but they are generally mild and will go away within a few days. You cannot pass these symptoms to others.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Michael Kopf, MD

Dr. Michael Kopf graduated cum laude from the University of Miami, where he majored in Film Studies and English Literature. He went on to receive his medical degree from Ross University School of Medicine. Michael trained in Internal Medicine at Danbury Hospital-Yale School of Medicine, and went on to complete fellowships in Hematology/Oncology at SUNY Downstate and Palliative Care at Memorial Sloan Kettering Cancer Center. In addition to his work in medicine, Michael enjoys watching and reading about movies, writing, and spending time with his wife and yorkie, Excelsior.

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