The Immune System—the Body’s Defense Against Infection
To understand how COVID-19 vaccines work, it helps to first look at how our bodies fight illness. 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. Blood contains red cells, which carry oxygen to tissues and organs, and white or immune cells, which fight infection. Different types of white blood cells fight infection in different ways:
Macrophages 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.
B-lymphocytes are defensive white blood cells. They produce antibodies that attack the pieces of the virus left behind by the macrophages.
T-lymphocytes are another type of defensive white blood cell. They attack cells in the body that have already been infected.
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.
The body keeps a few T-lymphocytes, called “memory cells”, that 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.
TYPES OF COVID-19 VACCINES
mRNA 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. (Pfizer, Moderna)
VECTOR VACCINES contain a modified version of a different virus than the one that causes COVID-19. Inside the shell of the modified virus, there is material from the virus that causes COVID-19. 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. ( AstraZeneca, Johnson&Johnson, Sputnik V)
INACTIVATED VIRUS VACCINE: Inactivated virus vaccine uses SARS-CoV-2 viruses whose genetic materials have been destroyed either by chemicals, radiation or heat. Thus they cannot replicate, but can still trigger an immune response to build up antibodies to fight against the disease. (Sinovac)
PROTEIN SUBUNIT VACCINES include harmless pieces (proteins) of the virus that causes COVID-19 instead of the entire germ. Once vaccinated, our bodies recognize that the protein should not be there and build T-lymphocytes and antibodies that will remember how to fight the virus that causes COVID-19 if we are infected in the future. (Novavax)
Currently, there are four main types of COVID-19 vaccines that has been approved by Thailand’s Food and Drug Administration (TFDA). AstraZeneca*, Sinovac , Johnson&Johnson and Moderna. Pfizer is under Thai FDA registration
* Siam Bioscience produce AstraZeneca Vaccine in Thailand
Source WHO, Yale Medicin, Biospace
