Is the Flu Shot a Live Virus? What to Know About the Flu Shot

Only the nasal spray vaccine contains a live virus, not the flu shot

The flu shot reduces your risk of contracting influenza, a virus that is common in the winter and causes coughing, aches, and fever. The flu vaccine can stop you from getting seriously ill or dying. Because of this, it’s recommended annually for all Americans who are 6 months or older.

Despite the prevalence of the flu shot, many people have unanswered questions about the flu vaccine, including: Is the flu shot a live virus? How effective is the flu vaccine? What are the flu vaccine side effects? 

There is only one type of flu vaccine—the vaccine administered as a nasal spray—that contains a live virus. That virus is attenuated (weakened) and cannot cause illness. 

This article will explain the live flu vaccine and answer common questions about the vaccine. 

child receiving vaccine
Cell-based flu vaccines are effective in children as young as two, according to new data.

History of the Flu Shot

The flu vaccine has been used for more than 80 years. Here’s an overview of its use over time:

  • 1940s: The flu shot is developed in 1940. Initially, it was only for army use, but by 1945, it was approved for civilians. 
  • 1960s: In 1960, the U.S. surgeon general recommends that all people with chronic diseases, people over the age of 65, or people who are pregnant get an annual flu vaccine. This was in response to a 1957 flu pandemic that killed 116,000 Americans. 
  • 1970s: Another flu outbreak leads to widespread vaccination, with about 25% of Americans getting the vaccine. 
  • 1990s: Federal programs, including Medicare, begin covering the vaccine, resulting in more use. 
  • 2002: The vaccine is recommended for babies ages 6–23 months.
  • 2003: The nasal spray flu vaccine is approved. 
  • 2012: The World Health Organization (WHO) recommends a quadrivalent vaccine, which combines protection against four flu strains. This is still used today.  

In the 1990s, the use of the vaccine became more widespread, in part because of federal programs that paid for vaccination. 

Common Myths About the Flu Shot

Although the flu vaccine has been used for decades in millions of Americans, there are many misconceptions. Here are the answers to common questions about the flu vaccine. 

Is the Flu Shot a Live Virus?

There is only one type of flu vaccine that contains a live virus: the nasal spray vaccine, sold under the name FluMist Quadrivalent. This vaccine contains live viruses, but they have been weakened and cannot cause illness. The nasal spray flu vaccine is approved for people ages 2-49. It cannot be given to pregnant people or those with compromised immune systems.

Flu shots do not contain a live virus. The shots are made either with a virus that has been killed or with a single protein of the virus.

Can the Flu Shot Get You Sick?

No, the flu shot cannot cause you to get the flu. If you experience the flu after getting your vaccine, you were likely exposed before getting your shot. It takes about two weeks after getting the vaccine to be fully protected, so you can still contract the flu during that time.

Although the flu shot can’t make you sick with influenza, it can lead to side effects. These are usually mild and include soreness at the infection site, aches, fever and feeling tired. In most cases these resolve within a day.

Do You Need a Flu Shot Every Year?

Yes, you should get the flu shot every year. The vaccine becomes less effective with time. In addition, the formulation of the flu vaccine is customized each year against the strains of the flu that are expected to be more common during that flu season.

Is the Flu Shot Effective?

When the viruses in the flu vaccine match the viruses that are circulating, the flu vaccine reduces your chance of catching the flu by 40%–60%. However, scientists can’t always predict what strains of flu will be most active, so sometimes the vaccine is less effective than that.

However, the vaccine is very effective at preventing hospitalization and death, as follows:

  • Vaccinated people who get the flu are 26% less likely to enter a hospital’s intensive care unit (ICU) for people who are very ill than unvaccinated people. 
  • Vaccinated people are 31% less likely to die from flu than unvaccinated people. 
  • Among people hospitalized for flu, vaccinated people are 59% less likely to enter the ICU.

Flu Shot Ingredients

Flu vaccines contain ingredients that provide immunity and keep the vaccine safe during manufacturing. The exact ingredients vary based on the vaccine you get, but in general, vaccines contain:

  • Portions of the virus that you are being protected against, to elicit an immune response
  • Preservatives and antibiotics, to keep the vaccine from being contaminated during manufacturing
  • Adjuvants, materials like aluminum, that help your body give a stronger immune response
  • Stabilizers, like sugar or gelatin, to keep the vaccine effective
  • Cell culture materials, like egg protein, that the virus has been cultured in (There are now egg-free vaccines available for people with severe egg allergies.)
  • Inactivating ingredients, which kill the virus (Formaldehyde is often used, but in such small concentrations that it is not harmful.) 

It’s important to remember that these ingredients are carefully screened for safety, and they are not linked with any ill health effects. If you have questions about vaccine ingredients, talk with your healthcare provider or pharmacist. 

Flu Shot Side Effects

The flu shot can’t make you sick, but it might make you feel under the weather for a day. Common side effects of the flu vaccine include:

  • Soreness, aches, and headache
  • Fever
  • Tiredness

If you get the nasal spray vaccine, you might also experience a runny nose, sore throat or cough. These side effects are caused by your body mounting an immune response. They’re usually mild and resolve within a day. 

Importance of Getting a Flu Shot

Although we’re all used to living with the flu, it has serious health implications. Getting the vaccine is a way to keep you and those around you healthy. Here’s why:

  • It reduces risk of infection: The flu vaccine reduces your risk of infection by up to 60%. That can help stop the spread to those you love and anyone you encounter.
  • It reduces severity of illness: If you do contract the flu, you’re less likely to need hospitalization. If you end up in the hospital, you’re less likely to need intensive care.
  • It can prevent complications from chronic health problems: People with heart disease are less likely to have a cardiac event when they’re vaccinated. Being vaccinated is also associated with fewer complications from diabetes and chronic lung disease.
  • It helps protect you during pregnancy: Getting vaccinated reduces the risk of a pregnant person being hospitalized for flu by 40%. The vaccine can also offer protection to the baby during the first few months of life, when a child is not yet eligible for vaccination.

Summary

Most flu vaccines do not contain a live virus. Only the nasal spray contains a live virus, and it has been weakened and cannot cause infection or illness. Getting the flu vaccine cannot cause you to get influenza. However, it can protect you from contracting the flu and getting seriously sick with it. 

A Word From Verywell

There’s a lot of misinformation floating around about vaccines. That can make it scary to get vaccinated, especially if you’ve already had the flu and recovered.

However, the flu causes tens of thousands of hospitalizations and deaths in America each year. The vaccine is the best way to protect yourself and those around you. If you have concerns about the flu shot or flu vaccine ingredients, speak with your healthcare provider or pharmacist, and have them answer your question. 

Frequently Asked Questions

  • What is the nasal flu vaccine?

    The nasal flu vaccine is a vaccine administered as a nasal spray. It’s approved for people ages 2–49. It’s the only type of flu vaccine that contains a live virus, but the virus has been weakened so that it can’t cause illness. Still, the nasal flu vaccine can cause additional side effects including sore throat and runny nose.

  • When did the flu shot stop using a live virus?

    The flu shot has never contained a live virus.

  • How effective is the flu shot?

    The flu vaccine is about 60% effective when there’s a good match between the viruses covered by the vaccine and those circulating. However, there’s not always a good match, so effectiveness has varied from 19 to 52% since 2012.

  • Is the flu shot safe to get?

    Yes, the flu shot is safe to get. It can reduce your risk of serious illness, and most side effects are mild.

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6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  4. Centers for Disease Control and Prevention. Key facts about seasonal flu vaccines.

  5. Centers for Disease Control and Prevention. Vaccine effectiveness: how well do flu vaccines work?

  6. Centers for Disease Control and Prevention. What’s in vaccines?