Vaccines Flashcards
Origin of vaccines
smallpox, vaccination with cowpox, Edward Jenner 1796, eradicated 1980
Vaccines and immune prophylaxis
Various strategies to induce immunity prior to pathogen exposure, by passive or active immunization, by natural processes (transplacental transfer of maternal IgG or prior infection) or by artificial means (injection of antibodies or vaccines).
Childhood immunization schedule in nova scotia
DTaP-IPV-Hib - 2 months, 4 months, 6 months, 18 months. Pneumo Conj - 2 months, 4 months, 12 months. Men C Conj - 12 months. MMRV - 12 months, 18 months, 4-6 year. Tdap-IPV - 4-6 years. Tdap, meningococcus, HPV, Hep B - 12 years.
Passive immunization
the administration of preformed antibody in order to give temporary protection against infection. Antibodies of maternal origin provide the newborn with a measure of protective systemic and local immunity. Pooled γ-globulin from horses immunized deliberately or humans immunized can be used to provide emergency protection for human beings when time does not allow for the development of adequate protection by active immunization. There is one approved monoclonal antibody on the market for passive immunization (Synagis®, palivizumab - used to prevent RSV infection in very premature babies).
Risks of passive immunization
Repeated administration of γ-globulin from foreign species can cause systemic anaphylaxis (Type I hypersensitivity) if IgE is made against the foreign protein. Human γ-globulin can trigger an anti-allotypic antibody response resulting in Type I or Type III hypersensitivity.
Active immunization
The aim of active immunization is to generate protective immunity and immunologic memory so that a subsequent exposure to the pathogen will stimulate a vigorous immune response leading to elimination of the pathogen. Active immunization can be achieved by natural infection or by vaccination. Not 100% effective.
Herd immunity
Indirect protection from infectious disease due to a large percent of the population becoming immune to infection. Essential to protect members of the population that cannot be vaccinated → newborns, pregnant or breast-feeding women, immune compromised.
How do vaccines work
Administration of antigenic material (biologic) to stimulate an individual’s adaptive immune response to a pathogen (without development of disease, memory immune response). Induction of B cell/humoral immune response (cytotoxic T cells can kill infected cells, prevent spread of infection).
What is an antigen
Any substance capable under appropriate conditions, of inducing a specific immune response and reacting with the products of that response; that is, with specific antibody or specifically sensitized T lymphocytes, or both.
The goal of a good vaccine
The objective of vaccination is to establish adequate levels of immune responses to protect against infectious agents. If the incubation period is short, it is important to maintain high levels of antibody by repeated immunizations since in such cases an infection could become established before memory B cells would be able to produce enough antibodies to have a protective effect. Antigens used as the basis for vaccine development must be readily available, stable, cheap and safe. The site of the immune response to the vaccine is important.
Examples of vaccine antigens
Poliovirus vaccines must contain T and B cell epitopes to generate humoral immunity (secretory IgA) against poliovirus (needs to be active in the gut, that is where it replicates). Only Th1 cells need to be activated in order to generate a protective DTH response against tuberculosis bacilli. To induce a protective immune response against measles virus, the pathogen must be allowed to undergo limited replication in host cells in order for viral antigen t
Live related vaccines
immunize with a closely related but much less pathogenic organism. Count on immunologic cross-reaction in response. Ex: cowpox (vaccinia) prevents smallpox (Jenner) - ”vaccinate”; leishmania major (skin) vs. leishmania donovani (viscera) - leishmanize. Positives: very strong protection, persistent antigen source, lots of antigens. Negatives: risk of serious infection, lack of availability of non pathogenic relatives to common pathogens.
Live attenuated vaccines
Concept: weak pathogenicity and growth ability (attenuate) of pathogen to allow for activation of immune response but not disease; attenuation achieved through chemical treatment, radiation or molecular manipulation. Ex: MMRV, flumist, oral polio (Sabin). Positives: persistence, full spectrum of antigens, humoral and cell mediated immunity, long lasting protection (limited boosting required). Negatives: risk of disease, care to not give to immunodeficient patients, require careful storage and handling.
Inactivated vaccines
Consist of microbes that are killed by heat or chemical treatment and are therefore unable to replicate but maintain their antigenic constitution and immunogenicity. Split virus: pathogen particles are inactiavted then disrupted with detergent or ether (reduces irritation). Ex: IPV (Salk), seasonal flu. Positives: very safe, wide spectrum of antigens. Negatives: no persistence, limited cell mediated immunity, often need adjuvant, boosting required, antigens damaged by treatment used to kill pathogen. Incomplete inactivation of the pathogen may lead to disease.
Sub unit vaccines
Isolated protein or recombinant protein derived from pathogen, often delivered with adjuvant commonly alum. Ex: Tdap/DTaP (diptheria, tetanus, pertussis), seasonal flu. Positives: very safe, easily transported and stored, used for organisms that produce potentially fatal toxins. Negatives: weak immunogen, needs adjuvant, needs boosting, no spectrum of antigens, transient (no persistence).
