How Vaccines Work

If you have ever participated in a fire drill, you already know how vaccines work. They prepare your body for a particular germ in the same way a fire drill prepares you for an actual fire. Let me explain.

Just as a fire could breakout to damage a building, germs can invade the body, multiply, and cause an infection. Some infections, like COVID-19, can be very serious.

The body has three main tools for fighting germs. Think of them as the fire alarm and the firefighter.

• White blood cells called macrophages swallow up and digest dead or dying cells along with the germs that infected them. They leave antigens behind. These macrophages are the early warning system. The body identifies antigens as dangerous and stimulates the next tool, the B-lymphocytes.
• B-lymphocytes are defensive white blood cells. They produce antibodies that attack the antigens left behind by macrophages. You can think of B-cells as the firefighters and all of their firefighting equipment. They get to the source of the fire and put it out.  
• Finally, there are T-lymphocytes. They attack cells in the body that have already been infected by the germ, just like a firefighter would look around to determine and neutralize the cause of the fire to keep it from starting back up.
• The immune system takes it a step further by leaving a few T-cells, called memory cells, behind to keep watch. It’s as if a firefighter is right there, ready and waiting, for a fire to break out! Impressive, immune system!  

If you have never practiced a fire drill, it may take you a while to know what you should do in case of fire. You may have to learn how to pull the alarm or call the fire department or track down a fire extinguisher. That’s just how your body feels when it’s under attack from a germ it has never seen. In fact, it can take the body a few days to get its tools—the macrophages, B-cells, and T-cells—working together to fight off the illness. By that time, we may be pretty sick.

Now, we wouldn’t set an actual fire to practice fire safety. That would be dangerous and irresponsible. In the same way, most vaccines don’t include the actual germ. They include something that, to the immune system, looks and feels like the germ. There’s lots more about how scientists produce something that looks and feels like the germ here.  

When you get the vaccine, the immune system gets its tools in order and deploys them, just as they would if the infection was real. So, if the germ shows up, they are ready. The immune system can take care of the germ right away, so it doesn’t make us ill or cause any damage. Just like fire drills, getting a vaccine is a simple safety measure we can all get behind.

Donna Barron, RN, is the infection preventionist at Southwestern Vermont Medical Center in Bennington.