Understanding the COVID-19 Vaccine, part 1: Immunology & Vaccine Basics


By now you’ve probably heard of the vaccines that have been produced for the COVID-19 virus. Maybe you even know someone who’s received it (like Cathy!). This is an exciting and promising step that can help us stop the spread of COVID-19 and protect those of us working on the front lines as well as our patients, friends, family, and loved ones. In this blog series, we will discuss what vaccines are, how a COVID-19 vaccine works, what side effects to look out for, and work to clear up some of the myths and misinformation that’s currently floating around about these immunizations.

What are antigens?

Your immune system is like a military force. Its job is to recognize and neutralize threats it encounters. Antigens are proteins found on the surface of cells or pathogens which the immune system looks for to identify what belongs in the body and what is a potential invader. You can think of antigens as being little identification flags that a cell or viral particle carries. You have antigens on your own body’s cells, which tell your body “Hi! I belong here!” so that your immune system will (usually) leave it alone. Antigens exist on cells and particles originating from outside your body, as well.

When a cell enters your body that does not belong there, its antigen (or “flag”) is used to identify it as an invader. B and T cells are a part of your immune system which are constantly on high alert, checking out antigens wherever they find them, hoping to identify antigens presenting on infectious agents in your body or on the surface of your own infected cells. When a cell in your immune system recognizes an antigen as being a threat, it alerts the rest of the “soldiers” in your immune system to mobilize and start fighting against the threat!

What are antibodies?

Antibodies protect your body! They are proteins that your immune system produces in order to fight against invading pathogens to keep you safe. It takes a while for your immune system to start pumping out antibodies the first time it encounters a pathogen, but the coolest part is that our body remembers what it’s fought against in the past.

That’s right! Your immune system has cells called “memory cells” whose sole job is to remember the viruses, bacteria, fungi, and other microbes it has encountered in the past so that it can quickly start fighting them if it encounters them in the future!

What are vaccines?

Now that we’ve refreshed your immune system knowledge a bit, let’s start to develop a framework for understanding how vaccines work! If you think back to the immunology chapters from anatomy and physiology, you might remember that we have a few different types of immunity. It can be active, passive, natural, or artificial. Vaccines are a form of artificial active immunity. This means your immune system actively fights against a perceived threat in order to create its own antibodies, but the threat was artificially created by way of a vaccine.

How do vaccines work?

The basic function of a vaccine is to introduce some component of a pathogen to your body. By allowing your immune system to recognize it as a threat it is able to create those memory cells. If you ever encounter that virus again in the future, your body is ready to fight! Remember: the first time your immune system encounters a threat, it takes a fair amount of time to recognize it, create antibodies against it, and neutralize it. The next time it sees that same threat, the response time is drastically reduced!

What are some types of vaccines?

There are many different types of vaccines. The type of vaccine you receive influences how it works.

Some vaccines provide your body with the actual virus itself but in a weakened (or “attenuated”) form. These are aptly named “live virus” vaccines and include vaccinations like MMR (Measles, Mumps, & Rubella) and Varicella.

Another type of vaccination is one where you are given an inactive form of the virus or bacteria. A good example of this one is Pertussis, sometimes known as “Whooping Cough.”

Yet another form of vaccination is a “toxoid” vaccine, which doesn’t actually provide you with a portion of the virus, but rather with a toxin produced by the virus, making you immune to the harmful part of the illness. Examples of toxoid vaccines include Diptheria and Tetanus.

There’s still another kind of vaccination you have likely received: biosynthetic vaccines. As the name implies, these are “synthetic” (or lab-created) substances that are very similar to the virus or bacteria, but not derived from the pathogen itself. The one you’re likely most familiar with is Hepatitis B.

And...drumroll please...there’s ONE MORE kind of vaccine! This is the mRNA vaccine that is being used for the first time in the COVID-19 vaccinations. In a later post, we will talk more about why it shouldn’t scare you that this is the first vaccine of its kind that utilizes this technology, and how truly incredible mRNA technology is! This vaccine works in a truly unique and fascinating way; it doesn’t actually provide your body with any form of the virus or antigens. Instead, it provides your cells with the messenger RNA (mRNA) which codes for the COVID-19 antigen, called a “spike protein.” Your body uses this mRNA sequence to pump out the antigen all on its own. Your immune system can then target and remember the antigen. How cool is that!?

What can be expected from a vaccine?

When we use artificial active immunity, we are actually calling upon our immune system to respond to a perceived threat. Those T and B cells are super smart, but not smart enough to know the threat isn’t actually real. They mount a full-force response to the newly introduced antigen, viral particle, or attenuated virus.

This is why you sometimes don’t feel so great after a vaccine! It’s not that the immunization gave you the virus or infection, but rather the symptoms you are feeling are the symptoms of a normal and healthy immune response to the vaccination itself.

Typical side effects of vaccines include fatigue, redness/swelling/soreness at the injection site, headache, muscle or joint pain, malaise (or just a general sense of feeling not so good), fever (again, remember--fever is a normal immune response!), and even swollen lymph nodes (especially near the injection site). Although these may be bothersome, these side effects should pass usually within 24-48 hours, and they can be treated with over-the-counter analgesics, rest, and increased fluids.

When should I call my doctor?

As with anything, there is always the risk of adverse or unexpected effects that are rare but life-threatening. If you develop a high fever, muscle weakness, or signs of an anaphylactic reaction (difficulty breathing, hives, itching, swelling of the mouth/tongue/lips/throat), seek care immediately by calling 911 or visiting your nearest emergency room. Again, reactions such as these are very rare but should be taken seriously! If you have any symptoms that concern you, calling your doctor is always the best move!

Back to blog


Thank you for this info! Can you speak to pregnant women getting the vaccine? It seems like based on the above information, it should be fine…but I keep sensing hesitation from others.


Great post Cathy, I really appreciate you breaking this down piece by piece. I am sending this to all of my informed family and friends! Happy Holidays!


Leave a comment

Please note, comments need to be approved before they are published.