How Does a Shot Protect You from the Flu?

Flu season has arrived and Minnesotans are making their annual pilgramages to vaccination clinics.

But how exactly does a simple shot in the arm or nose spray help your immune system protect you from nasty infections?

The flu shot is an example of what scientists call active immunization, which refers to administering a vaccine or toxiod (an inactivated toxin) in order to protect someone from a specific kind of infection. It is called active immunization, because it artificially triggers your immune system to make antibodies that allow your body to recognize and destroy an infectious agent, like a virus or bacteria.

When you are given a vaccine, an infectious agent, or part of one, is introduced into your body. Some vaccines are called “whole cell killed vaccines” and are made from attenuated (weakened) organisms or dead organisms. Other vaccines are “subunit vaccines” and contain small pieces of microbes that your body will react to.

When a vaccine enters your body, your immune system recognizes it as foreign and goes to work. After recognizing an antigen—or foreign agent—your body causes cells called B cells to divide rapidly. Some of these B cells become plasma cells, which pump out large quantities of antibody. 

Antibodies are proteins that help your immune system recognize and kill infectious agents, and each antibody is made to bind to one specific protein on a foreign substance. While it is active, a single plasma cell in your body can pump out as many as two thousand antibodies per second, each of them specific for the microbe you’ve been exposed to or vaccinated against!

In addition, your body makes what are called memory B cells, allowing your body to respond more rapidly the next time it sees the same microbe. Some vaccines require second or third doses in order to increase the number of antibodies and memory cells you have circulating around.

Once you have antibodies and memory cells to a microorganism, you can often avoid coming down with the disease you’ve been vaccinated against. At the very least, you will be able to fight it off better.

The flu is caused by the Influenza virus, which causes a miserable respiratory disease which can lead to hospitalization, and sometimes even death. 

Flu vaccine is made from the inactivated Influenza virus. Influenza is a master of disguise and changes its protein coat frequently, making it so that someone who has antibodies against its proteins one year may not have antibodies against its changed proteins the next. That's why you need a shot each year to help your body recognize and fight off the newest, circulating varieties of flu.

Each year, health experts take samples of flu viruses from around the world and use this information to engineer the next vaccine.

Although the vaccine we have now is far from perfect and may only protect you 6 out of every 10 times you are vaccinated, it is far better than nothing and saves countless lives. Vaccination helps protect the population as a whole, and it is essential that we continue our support of scientific research and public health organizations in their quest for better vaccines.