ABSTRACT
Many malariologists believe that different types of malaria vaccines may be necessary for different populations. Whether or not this turns out to be the case, we find it useful to think about the extremes of requirements for a malaria vaccine. One requirement is to reduce the incidence of severe malaria and malaria-associated mortality in infants and children with heavy exposure to Plasmodium falciparum, such as those living in sub-Saharan Africa (type 1 vaccine) (Table 13.1). At the other extreme is the requirement to prevent all clinical manifestations of malaria in individuals from areas with no exposure who travel to regions where malaria is endemic, primarily malaria caused by P. falciparum and P. vivax (type 2 vaccine). This ‘extremes’ approach to malaria vaccine development does not take into account specifically populations affected by malaria who fall between these extremes, particularly individuals in endemic regions at high risk of P. vivax infections. As type 1 and type 2 vaccines are developed, they will need to be assessed in many different types of populations. Models for malaria vaccine development
Vaccine
Goal
Primary target population
Model
Primary mechanisms
Antigenic targets
Type 1 vaccine
Reduce the incidence of severe malaria and malaria-associated mortality
Infants and children living in areas with significant exposure to P. falciparum
Naturally acquired immunity: No deaths or severe disease after 10 years of age Decreased incidence, prevalence and density of infection with age
Antibodies (CD4+ T cells)
Parasite proteins expressed on the surface of merozoites and infected erythrocytes (B-cell epitopes)
Type 2 vaccine
Prevent all clinical manifestations of malaria
Travellers to malaria endemic areas with little or no immunity to Plasmodium species parasites
Irradiated-sporozoite immunization: Greater than 95% protection Protection not strain-specific Protection lasts for at least 10 months
CD8+ T cells (antibodies, CD4+ T cells)
Parasite proteins expressed by irradiated sporozoites in liver cells (T-cell epitopes) Sporozoite surface proteins (B-cell epitopes)
