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(Target Population)

Type of Vaccine

Clinical Trial Difficulty

Rabies virus

(Individuals at high risk, plus post-exposure prophylaxis)

Vero cell

Little; depends on antibody response


Glycoprotein produced by rDNA technology in mammalian cells

Fatal natural disease and current availability of effective vaccine require rigorous proof of likely efficacy prior to field trials

(Birth cohort in areas of high risk)

Attenuated live vector virus containing gene for protective glycoprotein antigen

Some possible apprehension over new approach

Respiratory syncytial virus


Polypeptides produced by recombinant DNA technology

Difficult. Needed very early in life; need rapid response. Vaccines won’t take in persons with antibodies

Attenuated live virus



(Infants, 0–6 months)

Attenuated high passage bovine rotavirus

Relatively easy. Pathogen present everywhere in world. Can do trial in children<1 year

Attenuated low passage bovine rotavirus

Rhesus monkey rotavirus

Salmonella typhi

(Children; young adults at risk; travelers from developed countries to endemic areas)

Attenuated ga1E mutant S. typhi strain TY21a

Trials largely completed; further work needed to optimize vaccine

Aromatic amino acid dependent strains of S. typhi

Shigella spp.

(Infants at birth or earliest possible age; elderly for epidemic strains)

Probably plasmid mediated outer membrane protein invasion determinant (small number of promising options need investigation to determine best approach)

Moderate to difficult

Streptococcus A

(Children,<3 to 4 years)

Synthetic M protein segment

(excluding portions cross-reacting with human tissue)

Moderate to very difficult

Streptococcus pneumoniae


Conjugated polysaccharides, polyvalent

Requires high degree of patient and physician cooperation. Multitude of bacterial types creates problems of accurately determining vaccine efficacy

Vibrio cholera

(Children, especially <2 years)

Genetically defined live mutant V. cholerae (A−B+ or A−B−) with respect to toxin subunit synthesis

Difficult. Need large populations in hyperendemic areas. Screening possible in volunteers

Inactivated antigens

Difficult. Same problems as live

Yellow fever virus

(Young children)

Attenuated live virus produced in cell culture

Ethical problems in field testing an improved vaccine when an effective one already exists

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