This book explores the immune system, the role of specific immune cells, and how the new Covid-19 vaccines enhance your immunity and protect you from disease.

Immunity: How Covid-19 Vaccines Work

—Centers for Disease Control and Prevention: U.S. Covid-19 Vaccine Product Information. Visited 1-18-21. <a href="https://www.cdc.gov/vaccines/covid-19/info-by-product/index.html">https://www.cdc.gov/vaccines/covid-19/info-by-product/index.html</a> —Connors, M et al. SARS-CoV-2 vaccines: Much accomplished, much to learn. Annals of Internal Medicine 2021.<a href="https://www.acpjournals.org/doi/10.7326/M21-0111">https://www.acpjournals.org/doi/10.7326/M21-0111</a> —Corum, J and Zimmer, C. How the Johnson &amp; Johnson Vaccine Works. The New York Times, 02-27-21. <a href="https://www.nytimes.com/interactive/2020/health/johnson-johnson-covid-19-vaccine.html">https://www.nytimes.com/interactive/2020/health/johnson-johnson-covid-19-vaccine.html</a> —Corum, J and Zimmer C. How Moderna’s Vaccine Works. The New York Times, 03-22-2021 updated. <a href="https://www.nytimes.com/interactive/2020/health/moderna-covid-19-vaccine.html">https://www.nytimes.com/interactive/2020/health/moderna-covid-19-vaccine.html</a> —GAVI Covax Vaccine Roll-out. <a href="https://www.gavi.org/covax-vaccine-roll-out">https://www.gavi.org/covax-vaccine-roll-out</a> —Krammer, F. SARS-CoV-2 Vaccines in Development. Nature 586, 516–527 (2020). <a href="https://doi.org/10.1038/s41586-020-2798-3">https://doi.org/10.1038/s41586-020-2798-3</a> —Milken Institute: Covid-19 Vaccine and Treatment Tracker. Visited 3-26-21. <a href="https://covid-19tracker.milkeninstitute.org/">https://covid-19tracker.milkeninstitute.org</a> *Some graphics were built using <a href="https://biorender.com/">BioRender.com</a> online software.

B cells make antibodies that bind virus spikes

Spikes on the Covid-19 virus

After vaccination, if you are exposed to the real Covid-19 virus, your memory B and T cells will "recognize" and bind to the spike protein on the virus. This will activate the memory cells, which will rapidly multiply and aggressively respond by making antibodies, secreting potent stimulatory molecules (lymphokines) and killing infected cells—before you get sick!

Vaccines Teach the Immune Cells to Target Germs

The immune system normally can protect you from infectious diseases—however, some infections, like Covid-19, cause severe illness and even death before the adaptive immune system can halt the infection. That's why vaccines are created—they prevent infections and severe illness, and save lives.

Covid-19 virus particles. Image credit: National Institute of Allergy &amp; Infectious Disease.

The Covid-19 virus has protein spikes on its surface that facilitate entry and infection of human cells. People who recover from Covid-19 have antibodies in their blood that: 1) stick (bind) to the virus's spike protein, 2) block viral entry into cells and 3) eliminate the virus from their bodies. Therefore, scientists have created vaccines that teach the adaptive immune system to make antibodies and killer T cells that target the spike protein.

What are the Covid-19 mRNA and modified virus vaccines made of?

Modified Adenovirus Vaccine

Both Covid-19 mRNA vaccines are composed of fat (lipid) droplets filled with mRNA that codes for the harmless Covid-19 spike protein. The Covid-19 modified adenovirus vaccine is made from a non-replicating adenovirus carrying DNA that codes for the spike protein.

Illustration of muscle cells (pink) and macrophage cells (➜) taking up vaccine (yellow).

After a Covid-19 vaccine is injected into your arm, macrophage cells and other cells engulf the vaccine and begin producing the foreign spike protein (antigen).

Your immune system protects you from viruses, bacteria and other germs with its protective barriers, lymph organs and specialized immune cells, which are found throughout your body. Vaccines strengthen your immune system. Several new vaccine technologies are now being used in the U.S. to prevent Covid-19. Both the mRNA vaccine and the modified virus vaccine deliver the Covid- spike gene, as either mRNA or DNA respectively, and instruct your cells to build the foreign spike protein. The presence of the foreign spike protein activates your innate and adaptive immune systems and leaves behind memory immune cells in the body. After vaccination, if you become infected by the Covid-19 virus, your memory immune cells are rapidly activated and will eliminate the virus from your body before you get sick.

Tonsils Lymph Nodes Intestine Lining Skin

Thymus Spleen White Blood Cells Bone Marrow

White blood cells, found in your blood and in organs, play a key role in fighting infections. Bone marrow, found inside your bones, contains stem cells that produce new white blood cells (and red blood cells) when they are needed.

Have you ever wondered how your body defends itself against germs or how vaccines work? This book explores the immune system, the role of specific immune cells, and how the new Covid-19 vaccines enhance your immunity and protect you from disease.

Vaccines Teach Adaptive Immune Cells to Respond Rapidly

On day 1, you receive a first dose of the vaccine.

By day 7, your cells are making spike protein and your B and T cells are activated. Memory B and T cells remain in the body.

On day 21, you receive a second vaccine dose.

Timing varies; some vaccines do not require a booster.

By day 24, your cells are making more spike protein. Your memory B and T cells are rapidly multiplying and responding. Later, more memory B and T cells remain in the body.

Your first dose of vaccine "teaches" your naive B and T cells to become effective—but the response is slow (antibody levels peak at 7 days). Later, a portion of the immune cells will remain in your lymph organs as memory B and T cells. Your second vaccine dose causes the memory cells to respond rapidly to the foreign spike protein (antibody levels peak at 3 days) and this leads to a greater number of memory cells remaining in your body. This process is called priming the immune system or vaccination.

Your Innate Immune System is Always Present

Your innate immunity is always present and ready to fight foreign invaders. It includes natural barriers—like your skin and the mucous membranes of the nose, mouth, lungs and eyes—that prevent germs from entering your body. Innate immune cells have a variety of protective functions including: sparking a fever to fight off an infection, killing infected cells and tumor cells, and alerting the adaptive immune system (discussed later). Scavenger cells, like macrophage cells, continuously hunt for and engulf "foreign" germs (and debris) and then, activate the adaptive immune system.

Covid-19 Vaccines Mimic All or Part of the Virus

Modified Adenovirus Vaccine J&amp;J/Janssen

mRNA Vaccine Moderna Pfizer

Killed Virus Vaccine Weakened Virus Vaccine Purified Protein Vaccine

Two Covid-19 mRNA vaccines are U.S. Food and Drug Administration approved and one modified adenovirus vaccine is approved for emergency use in the U.S.. Over 270 additional Covid-19 vaccines are in development using these and other standard techniques—i.e. killed virus, weakened (live attenuated) virus and purified protein vaccines. For global vaccine distribution information, see <a href="https://www.gavi.org/covax-vaccine-roll-out">Gavi Covax</a> or the <a href="https://covid-19tracker.milkeninstitute.org/">Milken Institute treatment and vaccine tracker</a>.

The Adaptive Immune System Learns to Fight Germs

Your adaptive immune system includes specialized white blood cells, called B cells and T cells. They are activated by innate immune cells and must "learn" to attack specific germs. Therefore, your adaptive immunity is slower to respond. When B cells become active, they produce antibodies, which stick to germs or infected cells. This complex is removed from the body with the help of complement (part of the innate immune system). When T cells are activated, they kill infected cells and prevent the spread of infection, or they bolster the immune system by making stimulatory molecules.

Covid-19 Modified Adenovirus Vaccine Activates Immune Cells

Spike protein

When the modified adenovirus vaccine is taken up by the cells in your arm, the spike DNA is transcribed into spike mRNA. The spike mRNA provides the instructions needed to make the spike protein when it is loaded onto ribosomes. Spike protein is shuttled to the cell's surface where it activates your B and T cells (adaptive immune cells).

Deborah Landry, Ph.D. is founder and executive director of <a href="https://ixplorestem.org/">IXplore STEM</a>, a nonprofit formed to build science, technology, engineering and math (STEM) literacy and proficiency and to encourage K-12 students to pursue STEM degrees and careers. Dr. Landry has over 25 years of experience as a science teacher and curriculum developer for K-16 classrooms. She received her Ph.D. in Molecular and Cellular Biology from Brandeis University, focusing on genes in the immune system; and is an adjunct professor at the University of New England. In her spare time, Deborah enjoys exploring the woods and waters of Maine.

Covid-19 mRNA Vaccines Activate Immune Cells

When the mRNA vaccine is taken up by the cells in your arm, the spike mRNA is released inside the cell and is loaded onto ribosomes. The mRNA provides the instructions needed for the ribosomes to produce the spike protein. Afterwards, the spike protein makes its way to the cell's surface and finally, it activates your B and T cells (adaptive immune cells).

The immune system is a living shield that defends you against bacterial and viral infections and other diseases. It is made up of many organs and specialized immune cells.

The tonsils, located in the back of your throat, and the lymph nodes, located in your neck, armpits, groin, and elsewhere, have specialized immune cells that prevent infections. The lining of your intestines, mainly for digesting food, contains an enormous number of immune cells that protect you from germs. Skin is a flexible living barrier that prevents fluid loss, protects you from harmful things in your environment, and has immune cells roaming throughout it, hunting for invaders. The thymus, located above your heart, and the spleen, located in your abdominal cavity, both play an important role in producing immune cells.

After you recover from an infection, a portion of the activated B and T cells (that fought the virus or bacteria) remain in your lymph organs in a dormant state. They are called memory B cells and memory T cells. If you are exposed to the same infectious agent again, at a later time, your memory B and T cells respond more quickly and aggressively than the naive "inexperienced" B and T cells did during your first exposure. The memory cells rapidly multiply, migrate to the infection, attack the infectious agent and clear it from your body before you get sick.