Dengue virus

(Infants and children in endemic areas; travelers to endemic areas)

Attenuated live vector virus containing gene for broadly cross-reacting protective antigen

Phase I trials must be in adults, in nonendemic areas. Some apprehension over possible enhancement effects for dengue and with new approach

A combination of purified colonization factor antigens and possibly other antigens

Moderate. High attack rate in children and travelers makes evaluation possible in relatively small population. But may need to evaluate protection against certain serotypes or CFA types

Genetically engineered attenuated strains

Needs careful monitoring for reversion to virulence

Hemophilus influenzae type b

(Infants)

Conjugated polysaccharide

Need to be carried out in very young children

Attenuated live virus

Large number of subjects needed. Initial trials in adults may give false concepts of immunogenicity and reactogenicity for children

Polypeptide recombinant vaccine produced in yeast

Large number of subjects needed

Hepatitis B virus

(Areas with high perinatal infection: all infants at birth (if possible). Other areas: all infants, simultaneous with other vaccinations, at earliest possible age)

Polypeptide produced by recombinant DNA technology

Relatively simple

Japanese encephalitis virus

(Children in epidemic and endemic areas; foreign visitors to epidemic regions)

Inactivated virus produced in cell culture

Difficult. Low clinical attack rate requires very large number of subjects.

Mycobacterium leprae

(Immunoprophylactic: all children in endemic areas. Immuno therapeutic: all recently infected individuals)

Armadillo-derived M. leprae

Low incidence and long incubation period requires many subjects and long time for trials

Neisseria meningitidis

(Infants, 3 to 6 months)

Conjugated capsular polysaccharides, Groups A,C,Y, and W135

Difficult because epidemic disease is unpredictable

Parainfluenza viruses

(Infants)

Trivalent, subunit vaccine

(which must contain fusion proteins)

Plasmodium falciparum, synthetic or recombinant sporozoite antigen preparation

Mosquito challenge to volunteers

Multivalent synthetic or recombinant sporozoite antigen preparation

(P. falciparum, P. vivax, P. ovale, P. malariae)

Mosquito challenge to volunteers