The Flu Shot Can't Give You The Flu
Subunit and Inactivated Vaccines Explained With a Picture
Winter is coming, which means flu season is coming, which means you (yes, you) need to get the flu shot.
You might think you’re not at risk to catch the bug, or if you do you’ll fight it off and it won’t be that big of a deal. But regardless of your own risk, it’s important to immunize the maximum number of people to support what’s called “herd immunity.” Not because you’re a cow (although the word “vaccine” comes from the Latin word for cow 🐮), but because the more people get vaccinated the chance of a vulnerable person encountering an infected person moves closer to zero.
Who are those vulnerable people? Grandmothers & grandfathers, babies & people with compromised immune systems, to name a few. And those of us who are able to be vaccinated have an ethical responsibility to do so to protect those who are more vulnerable.
Unfortunately, I hear from many people that they choose not to get the flu shot for a variety of reasons, one of the most common being the fear that they could get the flu from the vaccine. I’m here to tell you that you can’t.
Flu Facts
The flu is a respiratory infection caused by members of the influenza virus family. During my PhD, I studied the immune response to influenza and novel flu vaccines, so I learned a little bit about this bug. Here are some fun facts to tell your Tinder date while encouraging them to get the flu shot:
- Influenza viruses are named for their “spike” proteins, which are the bits on the surface of the virus. These are Hemagglutinin (H) and Neuraminidase (N), which are given numbers based on their strains, together H1N1 or H3N2, etc.
- Influenza is an RNA virus with a segmented genome, which means its genetic information is carried on multiple molecules. This is crazy because it means that when two flu virus strains infect a cell, they can combine and create an offspring virus that is a mixture of the two co-infecting strains, which is basically virus sex; we call this reassortment.
- The process by which influenza viruses duplicate their genes is sloppy, and, combined with reassortment, allow the virus to mutate quickly. This fast mutation is one of the reasons you need a flu shot every year to target the new dominant strains.
I would love to go on with more #flufacts, but this article is about how you can’t get the flu from the vaccine, so let’s talk about why that’s the case and address some common reasons people think you can.
Flu=House, Inactivated=Rubble, Subunit=Brick
Chances are, you will get the standard trivalent vaccine, which means it is made up of three dominant strains. These strains are recommended by epidemiologists who monitor influenza circulating on the other side of the world (the southern hemisphere has the opposite flu season from us). The most common trivalent vaccines are inactivated, meaning they have been treated in a way that destroys the flu virus.
The rubble of a demolished house represents inactivated influenza vaccines, because, while all the parts of the virus are there, they have been destroyed beyond repair. Just as a house cannot reassemble itself from rubble, neither can influenza become a live virus from its broken, inactivated state. This is why you can’t get the flu from the inactivated vaccine.
Fortunately, you can get an immune response. Your immune system protects you by learning and recognizing the components of potential invaders and creating specific antibodies to fight them. When you are immunized with an inactivated vaccine, your body makes antibodies against the “rubble” (e.g., bricks, shingles), and these antibodies are able to protect you from the real thing, because just like an intact house is made of bricks and shingles, the intact virus has the same components as the inactivated one.
In contrast, subunit vaccines are made from isolated influenza proteins. Think of bricks as subunits. Subunit vaccines don’t contain broken viruses, they contain only specific parts, often the surface proteins: hemagglutinin and neuraminidase. Again, the immune response to the part (brick) gives protection against the whole (house).
Sure, these concepts make sense, but many vaccines are made from live viruses, right? And could a mistake happen that lets a virus slip by during preparation? No. Vaccines in the US and around the world are made to exacting “good manufacturing practice” standards in accordance with the FDA, and they are tested for live influenza virus, as well as a bunch of other potential contaminants depending on the production method. This insures the safety of these vaccines and that they can’t give you the flu.
There is one exception (and it’s not a flu shot): a live attenuated flu vaccine called FluMist, which is sprayed in your nose. FluMist does contain a live virus, but it is weakened (an old house?). Wikipedia has a good explanation here. However, the efficacy of this vaccine has become so low that the CDC does not recommend its use for the 2016 flu season.
Bottom line: if you get your flu vaccine as a shot, it can’t give you the flu.
Side effects
One reason people may think the flu shot can cause the flu is potential side effects. But these side effects are generally mild. For example, in a randomized placebo-controlled trial (the best kind of trial for this), the ONLY side effect detected was a sore arm (Nichol 2006).
I am one of those people who always gets a sore arm from the flu shot. But this soreness is reassuring to me because it lets me know that my immune system is responding to the vaccine. Other people report aches and mild fevers, and these are also likely due to immune activation. One of the earliest responses of the immune system is inflammation, and it’s this inflammation that you experience as soreness, achiness, or fever. I just take some ibuprofen, and the soreness goes away in a day or two. For those who really do get the flu right after getting the shot, the problem is you got vaccinated too late! You were exposed to a sick person before you were able to develop protective antibodies (which takes about two weeks), so don’t delay, get the shot as soon as it is available. By two weeks, you should have a robust antibody response, ready to protect you and those around you!
Other articles by @sciencethomas:
Antibodies: Friend & Foe
Think HIV is Cured? Not Yet
Fighting the Plague — A Story of HIV/AIDS
For more, follow me on Twitter @sciencethomas
Note: This and other things I write are my opinions about science and medicine, they should not be considered medical advice. If you have personal questions or concerns, talk with your doctor about these topics.
