There are several different types of vaccines. Each type is designed to teach your immune system how to fight off certain kinds of germs—and the serious diseases they cause, the available technology, desired strength of immune response and characteristics of the disease causing germ. Based on a number of these factors, scientists decide which type of vaccine they will make. There are several types of vaccines, including: Inactivated vaccines: These are vaccines derived from the germ that cause disease that has been destroyed/killed and unable to cause disease, reproduce or grow. Live-attenuated vaccines: These are vaccines derived from the disease causing germ that has been partially destroyed to limit their ability to cause disease, grow or reproduce. Subunit, recombinant, polysaccharide, and conjugate vaccines: These vaccines use specific pieces of the germ such as its proteins, sugar, or casing as signature that would trigger an immune response when introduced into a human body Toxoid vaccines: These vaccines use a harmful product (toxin) naturally produced by the disease causing organism. Examples include tetanus toxoid vaccine. Viral vector vaccines: These vaccines are made through use of a different virus, such as the adenovirus, that has been modified for the purpose of delivering genetic material for a desired viral antigen, such as the spike protein for SAR-CoV-2 virus, into the human cells. As a result the virus infected human cell receives the instructions and starts making the antigens against which the body mounts an immune response. Nucleic acid (Messenger RNA (mRNA)): These vaccines use a component of the virus (mRNA) which the virus uses to manufacture other molecules needed for its own propagation. When introduced into a human body through a vaccine, the viral mRNA instructs the human cells to make a protein that triggers an immune response just like a natural infection would. This approach is a new technology and has been used in some of the COVID-19 vaccines.