Bacterial Vaccines

Definitions

Immunization: protection from disease through deliberate stimulation of the immune response

not necessarily protection from infection
active: stimulation of body to develop its own defense
passive: introduction of Ig to provide temporary infection against disease

Vaccine: live or dead organisms, or parts of organisms, or toxoids to induce immunity

Toxoid: modified toxin (non-toxic) that stimulates formation of Ig against the toxin

Adjuvant: enhances the immune response when combined with vaccine (usually aluminum salt)

T-Cell Dependant Antibody Production: generally from protein antigens

induces immunologic memory, booster effects and immunogenicity even in young children

T-Cell Independent Antibody Production: generally from polysaccharide antigens

poor immunogenicity and booster effects in children less than 2 years old

Methods for Evaluation of Vaccine – immunogenicity, efficacy, safety

Variables Influencing Immunogenicity: age of vaccine; alteration of antigenic determinants by inactivation; biochemical composition of Ag (protein, polysaccharide); prior exposure to Ag or x-reactive Ag; presence of passively acquired Ab; immunocompetence of vaccine (e.g., immunodeficiency or immunosuppressive therapy)

Variables Influencing Efficacy: ability to induce antibody production (qualitative, quantitative); ability to provide herd immunity; ease of administration (storage, route of administration, number of doses)

Variables Influencing Safety: neutralization of virulence; cross-reactivity with human Ag; contaminants

Specific Vaccines

Bug	Vaccine Type	Immune Response	Immunization Age	Efficacy	Safety
diptheria	toxoid (inactivated protein toxin) – not to organism, therefore will not stop infection by organism	T-cell dependant	infancy	> 95%	most reactions local; rare neurological reactions
tetanus	toxoid (inactivated protein toxin)	T-cell dependant	infancy	> 95%	most reactions local; rare neurological reactions
salmonella typhi (typhoid fever)	live attenuated	not well studied; in theory all phases of immune response	travlers with prolonged exposure	50-70%	low incidence of side effects
pertussis (cellular)	inactivated whole cell vaccine	T-cell dependant	infancy; not > 7 years due to side effects	80% but short lived immunity	> 60% local infections and fever; possible CNS damage
pertussis (acellular)	inactivated subunit (69 kD protein, agglutinogens, or filamentous hemagglutinin)	varies depending on antigen used	infancy	variable depending on preparation used	fewer side effects than with cellular vaccine
pneumococcus	capsular polysaccharide from 23 serotypes – inactivated subunit	T-cell independent	> 2 years old booster every 6 years	estimated at 70% but is variable	mild local reactions in 50% severe reactions < 1%
Haemophilus influenzae type b (Hib)	polysaccharide-protein conjugate (PRP)	T-cell dependant	infants for conjugate; >2 if polysaccharide only	PRP-OMP and HbOC-PRP > 92%	local reactions < 4%

diptheria vaccine only induces antibody against the toxin; other effects of the bug can still occur (pharyngitis)

tetanus: requires 3 inoculations, booster every ten years; if injured and not immune administer Ig (passive immunity) - can vaccinate at same time (no problem with cross reaction)

salmonella typhi: immunization may be unprotective with ingestion of high inocula of organsisms

pneumococcus: indicated for patients > 65 (higher risk of infection)

immunocompromised are recommended also, but they are more difficult to immunize

live vaccines: very fragile and difficult to administer (no vomiting, diarrhea, antibiotics; heat labile; bad for immunocompromised patients)

Hib conjugates: kids < 2 cannot mediate effective T-independent responses; if the polysaccharide antigen is conjugated to a protein you can get T-cell dependant polysaccharide recognition

PRP-D-PRP: coupled to diptheria toxoid
HbOC-PRP: coupled to nontoxic mutant diptheria toxoid
PRP-OMP-PRP: coupled to outer membrane protein of Neisseria meningitidis
PRP-T-PRP: coupled to tetanus toxoid