Vaccine Types
Several types of vaccines can stimulate pathways involved in the innate and adaptive immune systems to help mount an immune response.
Live-Attenuated Vaccines
Live-attenuated vaccines contain a weakened form of the virus, which is not potent enough to make someone ill, but can still stimulate the body to produce an immune response. Live-attenuated vaccines cause a strong response and produce long term immunity with only one or two doses of a vaccine; however, they cannot be given to individuals with compromised immune systems because they contain a live form of the microorganism.
mRNA Vaccines
mRNA vaccines include messenger RNA, which acts as instructions to direct cells to synthesize a protein found on the virus. In the case of the Pfizer and Moderna mRNA vaccines, the cells are instructed to make the characteristic spike protein found on the surface of the coronavirus. After making the protein, the cells display the protein on their surface. The immune system recognizes the protein as foreign and begins making antibodies against it.
Killed or Inactivated Vaccines
Killed vaccines contain a pathogen that has been destroyed with chemicals, heat, or radiation. Though the microorganism has been killed, antibodies and T-cells can still recognize and bind to structures on the pathogen’s surface. This type of vaccine is much safer for individuals with compromised immune systems, however, they often produce a weaker immune response. As a result, several doses are often required.
Subunit Vaccines
Subunit vaccines contain only the parts of antigens that are recognized and bound by antibodies and T-cells. Though this type of vaccine only utilizes part of a pathogen, it is still a successful method to stimulate the immune response. These vaccines are usually safer but often require the incorporation of other components to elicit a strong protective immune response because the antigens alone are not sufficient to induce adequate long-term immunity.
Toxoid Vaccines
Toxoid vaccines contain inactivated bacterial toxins which are effective at eliciting an immune response against a particular bacterium, such as diphtheria or tetanus.
Prophylactic Vaccines vs. Therapeutic Vaccines
Prophylactic or preventative vaccines are administered to prevent a disease. The antigens introduced by a prophylactic vaccines will stimulate the pathways of the adaptive and innate immune systems to hopefully create long-term immunity. Most vaccines given to the public are prophylactic vaccines. Common prophylactic vaccines include the measles and polio vaccines, as well as the annual influenza vaccine.
Therapeutic vaccines are given to individuals after exposure to a microorganism. A therapeutic vaccine also contains antigens, but is intended to strengthen the immune response against an already present pathogen. One of the most well-known therapeutic vaccines is the Rabies vaccine.