How Does the COVID Vaccine Work?

COVID-19 vaccines work by helping the body develop immunity without having to first get the illness, which would naturally trigger the body's immune system to learn how to fight the disease.

The Centers for Disease Control and Prevention (CDC) explains: "Vaccines work with your immune system so your body will be ready to fight the virus if you are exposed.

"Protection from COVID-19 is critically important because for some people, it can cause severe illness or death," the CDC warned.

To know how a vaccine works, it's important to understand how our bodies fight illness. The CDC says: "When germs, such as the virus that causes COVID-19, invade our bodies, they attack and multiply. This invasion, called an infection, is what causes illness. Our immune system uses several tools to fight infection.

"The first time a person is infected with the virus that causes COVID-19, it can take several days or weeks for their body to make and use all the germ-fighting tools needed to get over the infection. After the infection, the person's immune system remembers what it learned about how to protect the body against that disease."

Most COVID-19 vaccines require more than one dose to be effective. "The first shot starts building protection. A second shot a few weeks later is needed to get the most protection the vaccine has to offer," the CDC said.

How blood cells fight infection

Our blood contains white or immune cells, which fight infection. Below are different types of white blood cells that fight infection in various ways:

  • Macrophages, which are "white blood cells that swallow up and digest germs and dead or dying cells. The macrophages leave behind parts of the invading germs called antigens. The body identifies antigens as dangerous and stimulates antibodies to attack them," according to the CDC.
  • B-lymphocytes, which are "defensive white blood cells" that "produce antibodies that attack the pieces of the virus left behind by the macrophages," the CDC explains.
  • T-lymphocytes, which are another type of defensive white blood cell that "attack cells in the body that have already been infected," the CDC adds.

T-lymphocytes, also known as memory cells, "go into action quickly if the body encounters the same virus again. When the familiar antigens are detected, B-lymphocytes produce antibodies to attack them. Experts are still learning how long these memory cells protect a person against the virus that causes COVID-19.

"It typically takes a few weeks for the body to produce T-lymphocytes and B-lymphocytes after vaccination. Therefore, it is possible that a person could be infected with the virus that causes COVID-19 just before or just after vaccination and then get sick because the vaccine did not have enough time to provide protection.

"Sometimes after vaccination, the process of building immunity can cause symptoms, such as fever. These symptoms are normal and are a sign that the body is building immunity," the CDC explains.

Types of COVID-19 vaccines

Below are the three main types of vaccines that have been undergoing trials. "None of these vaccines can give you COVID-19," the CDC said.

mRNA vaccines

These vaccines contain "material from the virus that causes COVID-19 that gives our cells instructions for how to make a harmless protein that is unique to the virus. After our cells make copies of the protein, they destroy the genetic material from the vaccine.

"Our bodies recognize that the protein should not be there and build T-lymphocytes and B-lymphocytes that will remember how to fight the virus that causes COVID-19 if we are infected in the future," the CDC explains.

Protein subunit vaccines

These vaccines include "harmless pieces (proteins) of the virus that cause COVID-19 instead of the entire germ. Once vaccinated, our immune system recognizes that the proteins don't belong in the body and begins making T-lymphocytes and antibodies. If we are ever infected in the future, memory cells will recognize and fight the virus," according to the CDC.

Vector vaccines

These vaccines contain "a weakened version of a live virus—a different virus than the one that causes COVID-19—that has genetic material from the virus that causes COVID-19 inserted in it (this is called a viral vector).

"Once the viral vector is inside our cells, the genetic material gives cells instructions to make a protein that is unique to the virus that causes COVID-19. Using these instructions, our cells make copies of the protein. This prompts our bodies to build T-lymphocytes and B-lymphocytes that will remember how to fight that virus if we are infected in the future," the CDC adds.

Johnson&Johnson COVID-19 vaccine trial December 2020
An investigational pharmacy technician at the Rocky Mountain Regional VA Medical Center holds a dose of a COVID-19 vaccine being developed by Johnson & Johnson before it is administered in a clinical trial in Aurora, Colorado on December 15. COVID-19 vaccines work by helping the body develop immunity without having to first get the illness. Michael Ciaglo/Getty Images

The wider picture

The novel coronavirus has infected more than 74.3 million people, including over 16.9 million in the U.S., since it was first reported in Wuhan, China.

More than 1.6 million people have died worldwide and over 42 million have recovered as of Thursday, according to John Hopkins University.

The graphic below, provided by Statista, shows the percentage of adults in the U.S. who would or would not get a COVID-19 vaccine.

COVID vaccine hesitancy in U.S.