It’s that time of year again.  The sequences are in, the Centers for Disease Control (CDC) have made their recommendations, and the vaccine has been prepared.  As an immunologist, I’m sad to say that I know far too many people who decide to forgo their flu shots each year.  When I ask why, I’ve gotten a variety of answers including:

“I never get the flu”  
“I once got flu from the shot”
“The flu shot never works, it’s just a guess”
And my all-time favorite:
“My body is stronger than the flu”

I’d like to set the record straight since each of these statements is ultimately and ridiculously flawed.

“I never get the flu” 
Flu is caused by a virus called influenza.  It’s been around, co-evolving with humans for as long as medical records have been kept.  In different forms it can infect a wide variety of animals from pigs to birds.  So, sure, it makes sense that influenza would specifically avoid you.  Just because you’ve never had the flu does not mean that you are naturally resistant.  It just means that you have been lucky (and you’ve likely had a few flu vaccinations in your lifetime).

“I once got flu from the shot”
There have been a few iterations of the flu vaccine over the years, but none of them cause flu.  There are 2 different vaccines that are given as a shot in the arm.  One is made up of dead virus.  Dead virus cannot cause disease.  The other one is called “live-attenuated”.  That one is technically living–as much as a virus can be considered alive (alas, a debate for another day).  But it has been weakened so that it cannot cause disease.  Plus, the vaccine is given in the arm muscle where influenza cannot infect nor grow.  Finally, the newest of the bunch is the live-attenuated nasal spray vaccine.  Oh no!  Now we have a live virus given access to the lungs??  The special attribute of this vaccine is that it has been modified so that it cannot cause disease.  So then you may ask, what causes you to feel sick after getting your flu vaccine?  Well, first it may just be a coincidence–association does not mean causation.  Secondly, when you are sick, many of the symptoms you experience are not caused by the pathogen at all, but are instead due to your immune response.  Fever, muscle aches, coughing, and runny nose are all caused by your body’s attempt to get rid of the invading microorganism. The point of a vaccine is to stimulate your immune system.  So, when you feel sick after getting a vaccine, this should be considered a good sign because it means that you are making an immune response to the vaccine!

“The flu shot never works, it’s just a guess”
To some extent, the components of the seasonal flu vaccine are a guess.  But an educated one made by expert virologists who study what types of influenza viruses people are infected with in each year.  To say this is a perfect process would be an outright lie.  However, even when the educated guess is wrong–as happened in 2014–getting the vaccine is still better than rolling the dice.  This is because the vaccine is made up of pieces from a few different influenza strains, which means that vaccine recipients may be partially protected.  That is, even though many more people got the flu in 2014, the disease tended to be more mild in a large proportion of patients.  Therefore, the vaccine is not all or nothing (protective or not), but can help minimize the duration or severity of flu symptoms.

“My body is stronger than the flu”
The hubris that surrounds this reason not  to get vaccinated astounds me above all others.  The fact is that there are millions of people that cannot get the vaccine for legitimate medical reasons.  That’s right, MILLIONS, therefore someone you likely know cannot get the vaccine!  These include patients with all sorts of conditions ranging from cancer to problems with their immune cells to having an allergy to vaccine components (including eggs).  Above all else, babies under 6 months old cannot get the flu vaccine.  The CDC reported that nearly 4 million babies were born in 2010.  So for any 6 months in 2010, 2 million babies were unvaccinated and susceptible to flu.

Think about it this way:  you go to a concert in a jam packed venue.  You are unvaccinated and therefore susceptible to disease.   More than 90% of the other people are vaccinated and therefore protected from disease.  A couple folks have an infection but don’t yet know it–a time in which they are highly contagious.  Unless you have contact with these infected people, an unlikely scenario given all the music fans in the venue, you won’t get infected.  Why?  Because all the other vaccinated individuals surrounding them prevented the spread of the disease to you.  This is called “herd immunity” and acts like an infection buffer zone.  But this scenario changes drastically if most of the other people are also unvaccinated like you.  The couple fans with the disease spread it to their neighbors, who then spread it to their neighbors, and so on and so forth.  [sidebar: did you ever stop to wonder where the internet term ‘viral’ came from?  yup]  Soon, the infectious pathogen has reached you.*

After the concert you go home to your family.  Perhaps someone else hasn’t gotten their vaccine because of a poor choice you’ve made for them, or maybe because they suffer from another condition that precludes vaccination, or maybe you have a newborn.  Guess what, you’re not invincible.  Even if you don’t get very sick from that infection because you’re so ‘strong’, you have played a pivotal role in spreading that disease to others.

Soon, I will have a niece born during this year’s flu season.  She cannot get her first flu vaccine until next spring.  For her sake, and for all the people out there who would get the vaccine if they could.  Go get your flu shot.

For more information, please visit:
History of Vaccines – Herd Immunity
Centers for Disease Control (CDC) – Key facts about seasonal flu vaccine

*This is an analogy and does not necessarily reflect the time frame that influenza would spread throughout a population at an event in a single evening.  However, it is useful imagery to depict how pathogens spread throughout communities at different thresholds of vaccination.  Please click on the History of Vaccines link above for a great animated version.