 In this video I will define active and passive immunity and describe how vaccines work. Immunity refers to protection from a disease, specifically protection from a disease that is a disease caused by a specific pathogen. Immunity could be passive immunity or active immunity. Active immunity is acquired from another person or another animal. Passive immunity means that while that person is protected, it's usually just a temporary protection because the adaptive immune response of that individual has not become activated and they did not develop the memory to antigens associated with that pathogen. Whereas an active immunity involves activation of the adaptive immune system by exposure to the antigen. You could either have a naturally acquired or an artificially acquired form of immunity whether it's passive or active. In the top left here we see the example of naturally acquired passive immunity where antibodies from the mother are transferred to a newborn through breastfeeding. Antibodies are secreted into the milk and then those antibodies provide some passive immunity to the child. Antibodies also are transferred from the mother to the fetus during development across the placenta. And so while the child is immune to the diseases that the mother was immune to as a result of the antibodies that were passed from the mother to the child, that's only temporary and the child's immune system has not formed a memory of the antigens associated with those pathogens. And later that child will be susceptible to those pathogens. They'll only be protected as long as they have their mother's antibodies in their body. So similarly there's the artificially acquired passive immunity where you can receive an injection of antibodies or an injection of blood. This injection will come from another person or an animal that has been exposed to the pathogen and already developed immunity. And so the naturally acquired active immunity is what occurs when you're exposed to the pathogen and then you develop the illness that results from that pathogen and then over time you recover from the illness but your adaptive immunity has formed a memory by exposure to the antigens that are associated with that pathogen then when a second exposure occurs the adaptive immunity is prepared to protect you from that pathogen. And so an artificially acquired active immunity will also stimulate the adaptive immune response in order to protect an individual for a long time. Vaccination is the main form of artificially acquired active immunity and a vaccine is in a weakened or attenuated form of a pathogen or a vaccine could just be an inactivated form of the pathogen or just a part of the pathogen it could just be a subunit of the pathogen maybe a protein or RNA from that pathogen can then function as a vaccine and the benefit of vaccination is that it stimulates immunity without the person having to suffer the illness that results from infection thousands of years ago long before we had developed vaccination people realized that some of the individuals that survived smallpox would become immune to smallpox and this led to the practice of deliberately inoculating individuals in order to protect them this practice is known as variolation so variolation involved deliberately exposing individuals with the infectious material that comes from these scabs or pustules of smallpox victims and usually people who are exposed to smallpox through variolation would survive and only develop a mild infection and then end up developing immunity to smallpox as a result and this is why variolation was a practice that was used for thousands of years however this was a somewhat risky practice because some percentage of patients that were exposed to smallpox would have developed a severe smallpox infection and some of those patients would have died from smallpox and so variolation was a early form of artificially acquired immunity the physician Edward Jenner depicted in the painting here was the first person to develop a modern vaccine Jenner observed that milk maids the women who milked cows were protected from smallpox and there was another disease known as cowpox that the milk maids were commonly infected with that transferred from cows to the milk maids so Jenner hypothesized that it was exposure to the cowpox that was protecting milk maids from smallpox in order to test this hypothesis Jenner acquired some of the material from a cowpox infected milkmaid so then he injected the pus into a child this caused the child to develop cowpox or to develop a mild infection from the cowpox virus and then later Jenner came back and exposed this child to smallpox deliberately to test and see if he would develop smallpox fortunately this exposure to cowpox protected the child from smallpox the child did not develop smallpox and this then led to the development of the smallpox vaccine which was widely used throughout the world and has led to the eradication of the smallpox virus later Louis Pasteur worked to develop several more vaccines for rabies cholera and anthrax and following that several others have worked on developing vaccines for a wide variety of infectious diseases including chickenpox hepatitis measles mumps polio yellow fever diphtheria pneumonia certain form of pneumonia bacterial pneumonia tetanus whooping cough and HPV the human papillomavirus that causes cervical cancer and other forms of cancer and so vaccination has become one of the most affected one of the most effective techniques in order to reduce the spread of infectious disease and the great benefit of vaccination is that it stimulates the adaptive immunity without requiring a person to go through the illness that would result from a primary exposure to the pathogen so vaccination works similar to the exposure to the pathogen that would occur naturally however with vaccination you don't risk developing the illness from exposure to the vaccine the immune system will still respond to the antigen that is contained within the vaccine and this will stimulate the adaptive immune response producing memory B cells through the process of clonal selection as well as plasma cells that will secrete antibodies of course these antibodies are not really needed to protect against the vaccine during the primary response to the vaccine but the individual is then protected so that if they're exposed to the pathogen in the future they will have a secondary response that involves the memory B cells recognizing the antigen of that pathogen and then rapidly producing plasma cells that can secrete antibodies similarly vaccination can stimulate the cell mediated immunity activating T lymphocytes so exposure to the antigen in the form of a vaccine can activate the production of memory T cells and then upon subsequent exposure to the pathogen in a secondary immune response the memory T cells will be able to rapidly produce cytotoxic T cells that can defend against that infection by destroying infected cells throughout the body