Understanding HPV Vaccines: Types and Responses

SCENARIO 2 Vaccines as Specific Antigens The government is holding an HPV (Human Papilloma Virus) immunization program for girls aged at least 11 years. The HPV vaccine is an active immunization that aims to induce the body's immunity to prevent infection with certain diseases. The vaccine is given by being injected intramuscularly several times at certain intervals. The HPV vaccine is a type of recombinant vaccine Know the types of vaccine preparations and how the body responds to various preparations vaccine. Tutor Instruction Questions LO 1: a. What are the types of vaccine preparations? b. How does the body respond to various types of vaccine preparations? There are now several basic types of vaccines. Some newer vaccines take full advantage of the knowledge and technology developed in recent years. Live attenuated vaccine In the fall of 1881 Louis Pasteur returned from his summer vacation and continued his studies of chicken cholera. The pathogenic bacterial culture he used (now called Pasteurella multocida) had been left on the bench over the summer. When he used this culture to inoculate some of the chickens that caused cases of chicken cholera, the animals remained healthy. Fresh pathogen cultures were then used to inoculate these chickens, but, surprisingly, they remained healthy. Pasteur concluded that the culture left on the bench that summer had weakened and was now unable to cause disease—but had made the chickens immune. From this chance observation Pasteur moved on to deliberately undermining experiments,attenuation, pathogens in various ways to determine whether a live attenuated vaccine can be created. Live vaccines, such as BCG are made from living (usually weakened) organisms. - Attenuated living organisms lose their ability to induce disease, but retain their immunogenicity - Attenuation is achieved by serially passing living organisms through a foreign host, such as a chick embryo/tissue culture or live animal. Note: Smallpox vaccine is a live, non-attenuated vaccine. Nonpathogenic cross-reactive vaccinia virus or cowpox virus is used to vaccinate against smallpox (i.e. variola) viruses. Profit Live vaccines are generally stronger immunization agents than killed vaccines, for the following reasons: - Living organisms reproduce in the host's body and the dose of antigen produced will be greater than that given - Live vaccines preserve all immunogenic components (major and minor) of the organism - Live attenuated vaccineis able to induce mucosal immunity by stimulating the production of secretory IgA antibodies at local mucosal sites Precautions When Using Live Attenuated Vaccines - Contraindications: Live vaccines should not be administered to individuals with immunodeficiency diseases or any condition that suppresses the immune system, such as leukemia, lymphoma, malignancy, on corticosteroid or other immunosuppressive drug therapy - Pregnancy is another contraindication, unless the risk of infection outweighs the risk of harm to the fetus by administering a live vaccine When twolive vaccinerequired to be given; The vaccine must be given at intervals of at least 4 weeks. The exception is vaccinesyellow feverwhich can be given less than 4 weeks after the MMR vaccine - Dosage: Most live vaccines are administered in a single dose because effective immunity is achieved with a single dose. An exception is the oral polio vaccine (OPV) which is given as multiple doses at certain intervals to achieve effective immunity - Risk of acquiring virulence: Attenuation of live vaccines must be done in an effective manner otherwise there is always a risk of regaining virulence. - Storage: Live vaccines must be stored carefully to maintain their effectiveness, especially OPV and measles vaccines. Inactivated killed vaccines Character ofInactivated killed vaccines: - Inactivated killed vaccinesgenerally safer but less effective than the live vaccine - Compared with live vaccines,Inactivated killed vaccinesrequires large doses, adjuvants, and several doses (boosters) to increase the body's immunity - Adjuvants increase the antigen immunogenicity of the vaccine (e.g. alum is used as an adjuvant in the DPT vaccine) - Inactivated killed vaccinesusually administered via subcutaneous or intramuscular routes. The only absolute contraindication is a severe local or general reaction to the previous dose. Subunit Vaccines Subunit vaccines use only antigenic fragments from microorganisms that best stimulate an immune response. This avoids the dangers associated with the use of live or dead pathogenic organisms. Subunit vaccines produced using genetic modification techniques, meaning that other microbes are programmed to produce the desired antigenic fraction—are called recombinant vaccines. For example, the vaccine against the hepatitis B virus consists of part of the virus's protein coat produced by genetically modified yeast.Toxoids, which are inactive toxins, are vaccines that target the toxins produced by pathogens—which can be thought of as subunits of the pathogen. Conjugated Vaccines Conjugated vaccines have been developed in recent years to address the poor immune response of children to vaccines based on capsular polysaccharides. Polysaccharides are T-independent antigens; Children's immune systems do not respond well to these antigens until 15 - 24 months of age. Therefore, polysaccharides are combined with proteins such as diphtheria or tetanus toxoid; this approach has resulted in a highly successful vaccine for Haemophilus influenzae type b (Hib), which provides significant protection even at 2 months. Nucleic Acid (DNA) Vaccines Nucleic acid vaccines, often called DNA vaccines, are one of the newest and most promising vaccines. Experiments with animals show that "naked" DNA plasmids injected into muscles result in the production of protein antigens encoded in the DNA. The injection can be done with a conventional needle or, more efficiently, with the "gene gun" method, which delivers the vaccine to many skin cell nuclei. Protein antigens are carried to the bone marrow and stimulate humoral and cellular immunity.