Two Flu Myths

“How I learned to stop worrying and love the shot”

Another year, another flu season! With each passing month, we get closer to the end (although we may have a late second peak according to Time Magazine! Toward the end of flu season, I like to revisit some of the conversations I had about the flu vaccine: what were common concerns, what did I say in response, and what  up-to-date evidence is available. Two major points seemed to be a rationale some of the families took to decline the flu vaccine: (1) the flu vaccine gave me the flu and (2) the flu vaccine doesn’t stop the flu.  Here are some effective talking points for pediatricians to discuss flu vaccination with patients and their families who have those concerns.

“The flu vaccine gave me the flu.”

I’ve heard this sentiment echoed hundreds of times and it simply isn’t true. The injectable flu vaccine (“flu shot”) is an inactivated (“killed”) vaccine. It’s made by growing influenza virus in a lab, killing it using heat or chemicals then using those killed viruses/viral particles to produce the vaccine ( When the body encounters the killed virus/viral particles, it responds and is primed to fight the real flu virus through primed recognition. The inactivation of the virus during production makes it impossible for it to reproduce, so it is unable to infect the body. 

The nasal spray (“flu mist”) vaccine is a ‘live-attenuated vaccine’, which is made of flu virus that is able to reproduce, but is in a weakened state ( The idea behind these vaccines is the presence of replicating virus allows for a strong and lasting immune response, just like with a normal infection, but producing minimal/no infectious symptoms. While there is a theoretical risk of the vaccine mutating to re-gain its ability to cause infection (called ‘reversion’), this has never been observed clinically with influenza vaccination and is such a small risk that it is considered negligible (Murphey and Coelingh, 2002Zhou et al., 2016). However, if this miniscule risk still worries  parents, pediatricians can explain that there is NO risk for reversion with inactivated vaccine (the “flu shot”).

What people may have experienced in the past is either a reaction to the flu vaccine, or infection with flu prior to mounting a full immune response after vaccination. With vaccination, there is always a possibility of a minor immune reaction. This typically consists of headache, fever, or pain/soreness/redness at the injection site. These are thought to be caused by the “priming” of the immune system in response to encountering viral particles. It’s essentially the body using the vaccine as a punching bag in anticipation of the real thing! These minor reactions are considered common, last typically between 24-48 hours, and can be treated with antipyretics and NSAIDs (

As I have often seen, families will wait until someone close to them gets the flu prior to seeking vaccination. While I will never stop my patients or their families from receiving the flu shot, waiting until someone is sick can be too late fora response from the vaccine. It’s estimated that it takes up to two weeks for the flu vaccine to take full effect, so getting vaccinated early is the best strategy. Immunity is estimated to last between 5-6 months after it takes effect; getting it early means you’re protected for the duration of flu season ( If a patient got the flu vaccine in response to seeing a nearby outbreak, then got the flu, the patient likely had  already been exposed, and the vaccine didn’t have enough time to take effect.

“The flu vaccine doesn’t stop the flu.”

For any patient or parent who says  this, I always respond, “Well you’re right! But not entirely.” While it is true getting a yearly flu vaccination doesn’t 100% prevent a personfrom getting influenza, it does significantly cut down on infections. During 2017-2018 flu vaccination prevented an estimated 6.2 million influenza illnesses, 3.2 million influenza-associated medical visits, 91,000 influenza-associated hospitalizations, and 5,700 influenza-associated deaths (

The CDC estimates a 40-60% risk reduction of having a symptomatic influenza infection after vaccination ( This estimate also assumes a good match between circulating seasonal flu and the four influenza strains used in the yearly vaccine. One of the major challenges of yearly flu vaccination is that it’s a moving target. Influenza viruses are constantly recombining and changing, so it’s not feasible to have a vaccine that targets them all. So could a person be the unlucky one who gets a strain that’s not covered? It’s absolutely possible. This fact alone can make many people feel apathetic about flu vaccination.

More recently my responses have shifted from “the flu vaccine stops you from getting the flu” to “the flu vaccine reduced severity of flu symptoms, even if you end up getting it”. This shift has mainly been driven by my patients and their parents reading about flu vaccination and being concerned about the shortcomings that it has. But many people are surprised to hear me say that flu vaccines have been shown to reduce severity of flu illness. Strong and ever-growing amount of evidence back this claim:

For adults, flu vaccinations:

  • Reduced deaths, intensive care unit (ICU) admissions, ICU length of stay, and overall duration of hospitalization among hospitalized adults with flu (Arriola et al., 2017; Thompson et al., 2018)

For kids, flu vaccinations:

  • Reduced a child’s risk of dying from flu (Flannery et al. 2017)
  • Reduced children’s risk of flu-related pediatric intensive care unit (PICU) admission by 74% during flu season (Ferdinands et al, 2014)

For pregnant mothers, flu vaccinations:

  • Feduced a pregnant woman’s risk of being hospitalized with flu by an average of 40% (Thompson et al., 2019)
  • Reduced the risk of flu-associated acute respiratory infection in pregnant women by about 50% (Thompson et al., 2019)
  • Helps protect their babies from flu illness for the first several months after their birth, when they are too young to get vaccinated (Madhi et al., 2014)

While it can be a long and sometimes frustrating conversation to have with  patients and their parents about flu vaccination each year, I hope the above statistics and citations can help inform  future conversations. I’ve had more than a few parents change their minds on flu vaccinations this year after discussing what I’ve outlined. You never know what kind of conversations you may spark by being the expert in the room!

Michael Hook, M.D.


1. Ferdinands JM, Olsho LE, Agan AA, Bhat N, Sullivan RM, Hall M, et al. Effectiveness of influenza vaccine against life-threatening RT-PCR-confirmed influenza illness in US children, 2010–2012. The Journal of infectious diseases (2014) 210(5):674-83.

2. Arriola C, Garg S, Anderson EJ, Ryan PA, George A, Zansky SM, et al. Influenza vaccination modifies disease severity among community-dwelling adults hospitalized with influenza. Clinical Infectious Diseases (2017) 65(8):1289-97.

3. Madhi SA, Cutland CL, Kuwanda L, Weinberg A, Hugo A, Jones S, et al. Influenza vaccination of pregnant women and protection of their infants. New England Journal of Medicine (2014) 371(10):918-31.

4. Flannery B, Reynolds SB, Blanton L, Santibanez TA, O’Halloran A, Lu P-J, et al. Influenza vaccine effectiveness against pediatric deaths: 2010–2014. Pediatrics (2017) 139(5):e20164244.

5. Thompson MG, Kwong JC, Regan AK, Katz MA, Drews SJ, Azziz-Baumgartner E, et al. Influenza vaccine effectiveness in preventing influenza-associated hospitalizations during pregnancy: a multi-country retrospective test negative design study, 2010–2016. Clinical Infectious Diseases (2019) 68(9):1444-53.

6. Thompson MG, Pierse N, Huang QS, Prasad N, Duque J, Newbern EC, et al. Influenza vaccine effectiveness in preventing influenza-associated intensive care admissions and attenuating severe disease among adults in New Zealand 2012–2015. Vaccine (2018) 36(39):5916-25.

7. Murphy BR, Coelingh K. Principles underlying the development and use of live attenuated cold-adapted influenza A and B virus vaccines. Viral immunology (2002) 15(2):295-323.

8. Zhou B, Meliopoulos VA, Wang W, Lin X, Stucker KM, Halpin RA, et al. Reversion of cold-adapted live attenuated influenza vaccine into a pathogenic virus. Journal of virology (2016) 90(19):8454-63.


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