International Development (USAID), the Noguchi Memorial Institute of Medical Research in Accra, Ghana, and the Navrongo Health Research Centre in Navrongo, Ghana. Experimental development of the MuStDO vaccine is currently focused on 15 P. falciparum antigens (5 pre-erythrocytic and 10 erythrocytic proteins) (Kumar et al., 2002), although future versions also may incorporate transmission-blocking antigens.

Practical Realities of Vaccine Testing and Use

Selecting which malaria antigens should enter clinical trials was not a major problem when there were relatively few candidates to choose from. However, characterization of the P. falciparum genome has now identified hundreds of parasite proteins that could potentially be tested as individual vaccine components. Selecting future vaccine components should rest upon: 1) evidence that the antigen plays an important role in the survival or pathogenicity of the parasite; 2) evidence from animal experiments that the antigen induces protective immunity in vivo; and 3) evidence that immune responses to the antigen are associated with protection (Greenwood and Alonso, 2002). If a vaccine candidate passes Phase I and Phase II testing, further considerations in designing phase III trials include study site, study population, study size, and appropriate clinical end points (Table 8-3). Another important factor that will influence whether a partially effective malaria vaccine is introduced into routine use will be its cost effectiveness relative to other malaria control measures, such as ITNs (Graves, 1998; Goodman et al., 1999).

TABLE 8-3 Possible End Points for Phase-III Malaria Vaccine Trials

End Point

Advantages

Disadvantages

Death

Most important public health end point

Requires large trial

Malaria mortality rate

 

Difficult to measure

Severe clinical malaria

Important end point

Requires high hospital admission rate

Mild, clinical malaria

Requires relatively small trial

May miss an effect on severe disease

Parasitemia

Easy to measure

May miss an important clinical effect

 

SOURCE: Greenwood and Alonso (2002).



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