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Debunking myths about flu vaccines

With flu season approaching, we asked Dr. Troy Sutton, one of VIDO's newest scientists, to help answer some common questions about flu vaccines. Troy brings years of experience studying influenza viruses and developing vaccines, and he's sharing his expertise to help separate fact from fiction.

By Dr. Troy Sutton
As a scientist studying flu viruses and vaccines, I am often asked about flu outbreaks and vaccines by family and friends. With influenza (flu) season just around the corner, it is important to understand just how big a problem flu can be. The World Health Organization estimates that 1 billion people become infected with influenza each year, and 3-5 million people become severely ill resulting in 290,000 – 650,000 deaths. 
 
Importantly, children play a major role in transmitting and spreading the flu, and children under 5 years of age, pregnant women, and older adults are most at risk of developing severe illness. With children back in school and the weather cooling, we spend more time indoors creating the perfect environment for flu viruses to spread.
 
While it sounds cliché, there is lots of scientific evidence showing that flu vaccines are the best way to protect yourself, your children, and others from the worst outcomes of flu infection. However, flu vaccines sometimes get a bad reputation because we seldom discuss how they work and what they do and don’t do. To help clarify how flu vaccines work, and their risks and benefits, I wanted to correct some common myths and misconceptions. 
 

Myth #1: Flu vaccines do not work

Like most vaccines, flu vaccines are given as an injection in your arm. Injecting a vaccine in your arm induces an immune response composed of antibodies in your blood. Antibodies are proteins made by your immune system that recognize and attach to viruses. You can think of them like little soldiers that grab onto viruses and prevent them from infecting you, or mark viruses for elimination by your body. When a vaccine is given in your arm, the antibodies produced circulate in your blood and enter the lungs and internal organs.
 
Unfortunately, these antibodies do not easily enter your nose and throat and since that is where flu viruses first enter your body and replicate, it is still possible to become infected after vaccination. However, once you are infected, there are changes in your body that allow antibodies to enter your nose and throat. In the case of the flu, while vaccines do not always prevent you from becoming infected, they can limit virus replication, decrease the likelihood that you will transmit the virus to others, reduce the severity of illness, and shorten recovery time. Thus, getting the flu after you have been vaccinated does not mean the vaccine did not work, instead it means the vaccine is working differently than many people expect.
 
A severe flu infection occurs when the virus moves into the lungs, which is a particular risk for young children, the elderly, and immunocompromised individuals. For these individuals, the major benefit of flu vaccines is that because antibodies can enter the lungs, they can prevent the virus from infecting your lungs and reduce the chances you get severely ill and require hospitalization. 
 

Myth #2: I don’t need a flu vaccine because I am young and healthy.   

For most adults that are healthy, getting infected with flu is unlikely to cause serious long-term health problems. However, you will likely be sick for 5-7 days, and it can take several weeks to feel fully healthy again. Getting a flu shot can reduce how long you are sick.
 
Outside of your own health, getting the flu shot may protect others that are close to you and at higher risk from getting seriously ill. For example, if you interact with young children or older adults, or if you work or play sports or do activities with groups of people of any age, then getting the flu shot can reduce the likelihood that you will pass the viruses on to others.
 
People that are very young, very old or that have other health complications such as diabetes or autoimmune diseases, can become severely ill when they contract flu, getting your flu shot may help protect them as well.
 
The end result is that getting your flu shot may improve your health and that of those around you as well. 
 

Myth #3: All flu vaccines are the same

While it may appear that all influenza vaccines are the same, there are actually several types of flu vaccines and the one recommended for you can depend on factors such as your age and health. The most common and well-recognized vaccine is an inactivated vaccine administered by injection into your arm. These vaccines are suitable for all individuals 6 months of age and older. Each vaccine targets three different flu virus strains.
 
For individuals 65 years and older, there are specially formulated vaccines that either contain a higher dose of vaccine or an extra component that helps the immune system respond to the vaccine. These vaccines have been developed because individuals 65 years and older do not always develop a strong immune response to regular flu vaccines.
 
It is best to discuss the different vaccines available with your pharmacist or physician as they can provide the most up-to-date information about which option is right for you. Importantly, all the vaccines have been shown to be safe.
 

Myth 4: Scientists are just guessing which flu strains to put in the vaccine.

Influenza vaccines target three different virus strains. One H1N1 influenza A virus strain, one H3N2 influenza A virus strain, and one influenza B virus strain. Because so many people get infected with flu each year, flu viruses mutate to avoid being recognized by the antibodies people develop after an infection. To keep up with these ever-changing viruses, flu vaccines are reformulated every 1-3 years to match the viruses that are predicted to circulate in humans during the next flu season. This is part of the reason why it is recommended that you receive your flu shot each year. For more details on the vaccine strain selection process check out our story about How Flu Vaccines Strains are Chosen Each Year.
 
Selecting the virus strains targeted by the vaccine requires a global research effort and the strains targeted by the vaccine are not always a perfect match. However, even when flu vaccines are not a perfect match, the antibodies induced by these vaccines often still prevent against severe disease and death. Thus, even in years when the vaccine is not a good match, it can still provide some protection.
 
I like to tell my friends and colleagues, while flu vaccines may not completely protect you or keep you at the bar, they can keep you out of the hospital. 
 

Myth #5, not actually a myth: What’s in a flu vaccine and how is it made?    

This one isn’t really a myth, but I get a lot of questions from friends and family, so I wanted to include an explanation about how the flu vaccine is made and its ingredients.
 
The most widely used flu vaccines are called inactivated split-virion vaccines. Which sounds fancy but it is just describing how the vaccine is made. In this case let me explain it using a balloon as an analogy. Influenza viruses are like little balloons, and the surface of the balloon is the part of the virus targeted by the immune system. On the inside of the balloon are the parts of the virus that are required for the virus to grow and make you sick.
 
Split-virion vaccines are generated by growing the three separate viruses that are eventually combined to make up a single vaccine. Each year experts choose one H1N1 influenza A virus strain, one H3N2 influenza A virus strain, and one influenza B virus strain, see the answer to Myth #4 for more details. These viruses are grown in eggs or cells and then treated with a chemical to kill the parts of the virus inside the balloon that allow the virus to replicate. Next, the viruses are purified to remove the chemical that killed the virus, and the virus is treated with a detergent (similar to soap) to break apart the surface of the balloon into smaller fragments. These smaller fragments of the balloon surface are then purified again, removing the detergent and unwanted parts of the virus.
 
After extensive testing the three different inactivated viruses are combined into a single vaccine. Importantly, every step of the vaccine manufacturing process is highly regulated, and throughout the entire manufacturing process, tests are performed to verify that chemicals are removed and that the composition of the vaccine is correct.
 
You can find information about the specific ingredients authorized for use in vaccines in Canada here.


Myth #6: The flu vaccine can give you the flu 

It is common to experience some mild side effects after getting a flu vaccine. Your arm may be sore where you received the injection, and some people may experience symptoms such as a headache, muscle aches, fatigue or a mild fever. These are signs that your immune system is responding to the vaccine and they usually go away within a few days. It is also important to mention that it takes up to three weeks for the vaccine to induce antibodies that can fight the flu virus. Thus, shortly after getting vaccinated, you have minimal protection from flu. In addition, your flu vaccine does not protect against other viruses that make you sick such as COVID or cold viruses. So developing a cold or flu shortly after getting your flu shot, can result from either your body not yet developing an immune response to the flu vaccine or another type of virus infecting you. 
 
We also know the inactivated flu vaccines given by injection cannot give you the flu because the flu viruses used to make them have been killed and broken apart. While serious reactions to flu vaccines can occur, they are rare. As with any vaccine or medication, it is important to understand both the potential benefits and risks, and to talk to your health-care provider if you have questions or concerns.

 

I hope this information helps answer some of the common questions about flu vaccines. For what it’s worth, my family and I get our flu shots every year.
 
And since I’m a scientist and we always cite our references, here are the resources I used to put this together. If you’re interested in learning more, I encourage you to explore the links below.
 
References: