In this session, we will describe the basis of a vaccine and the process of vaccination, the administration of vaccines. Upon completion of this module, you will understand the fundamental principles of vaccination and vaccine development, antibodies and passive immunization. Be able to describe the drug development process, clinical trials phases, and the state of COVID-19 vaccine candidates. Understand how the novel coronavirus that causes COVID-19 spreads from person to person and how mitigation strategies can help prevent the spread. To begin, it is important to define and distinguish two terms, SARS-CoV-2 and COVID-19. SARS-CoV-2 is the scientific name of the actual coronavirus that causes disease. COVID-19 is the disease caused by SARS-CoV-2. Vaccination is the process of administering a vaccine. As stated in the current slide, the fundamental principle of vaccination is the administration of an infectious agent that has been killed or made to be non-infectious or a part of a microbe that does not cause disease but that elicits an immune response which provides protection against infection by the live infectious microbe. But what exactly is a vaccine? A vaccine is essentially a microbe such as a virus or bacteria or a component of that particular microbe that does not cause disease because it has been killed or attenuated. Although this non-infectious microbe no longer causes disease when administered, it will activate the immune system to produce antibodies that protect the person against the live pathogen. This activation of the immune system and production of antibodies leads to long-term immunity and protection from the live infectious agent. Thus, the goal of a vaccine is to mimic our natural immune system and induce the production of antibodies that would protect us from the infectious virus or bacteria. We then can say that vaccination is the manipulation of our immune system under controlled conditions. That is, the use of a non-infectious agents to induce the production of antibodies just as an infectious agent would do, but without causing disease. Antibodies are proteins that are produced by specific immune cells in response to infection by a microbe. As shown in this figure, antibodies expressed to microbe binding sites that can bind to the microbe for which they were produced. For example, when a person is infected with the microbe like SARS-CoV-2, our immune system response by producing antibodies that can specifically bind to a specific part of SARS-CoV-2. The ability of antibodies to bind microbes enables them to carry out their most basic and primitive functions, which is to neutralize microbes and prevent them from infecting cells. As shown in this figure, in the absence of antibodies, microbes are freely able to bind to receptors on the surface of cells allowing them to enter and infect those cells. On the other hand, antibodies when present can bind to and coat the infecting microbe. By coating the infecting microbe, antibodies prevent that microbe from interacting with the receptors on target cells, effectively neutralizing or blocking the microbe from infecting those cells. A vaccine against COVID-19 will be a non-infectious SARS-CoV virus or component of the virus that does not cause COVID-19, but if successful will lead to the production of antibodies against SARS-CoV-2. Over time a successful vaccine, because of its ability to induce specific antibodies will lead to long-term immunity against this particular coronavirus that will provide protection from future infections with this virus string. A serological test is a test to determine if a person has antibodies against an infecting microbe. For example, a positive serological tests for SARS-CoV-2 means that the person has antibodies against SARS-CoV-2 in their bloodstream. This test is also used to determine if a vaccine is successful, since successful vaccines lead to antibodies production. Since there is currently no vaccine for COVID-19, a positive test for SARS-CoV-2 antibodies means that the person has previously been infected with the SARS-CoV-2, has produced antibodies and therefore has developed immunity. Immunity means that the patient is protected from future exposures to SARS-CoV-2. Since there is currently no vaccine against COVID-19, one strategy to treat patients infected with SARS-CoV-2 is to transfer antibodies from a person who has previously been infected with the virus but no longer has the virus in their body to a person who has COVID-19. This form of immunization is termed passive immunization, because passive immunization does not activate the recipient's immune system to produce their own antibodies. This form of immunization does not lead to long-term immunity. It is effective only for as long as the transfer antibodies remain in the body of the recipient. The development of a vaccine against COVID-19 is providing many medical and research challenges. However, we know from historical examples such as smallpox, which was eradicated following the discovery of vaccines and the process of vaccination, that vaccines are the most effective strategy to prevent disease.