Volume 50, Issue 2
  • ISSN: 0002-9637
  • E-ISSN: 1476-1645



Malaria epidemiologic and entomologic studies were performed during both the high transmission and low transmission seasons to characterize the malaria transmission at a proposed malaria vaccine trial site in Irian Jaya, Indonesia. The study population consisted of two subsets: native Irianese men with lifelong exposure to malaria and transmigrants who arrived from a nonmalarious area 2.5 years before the start of the study. All subjects received a radical cure for malaria and were then monitored weekly by blood film. Both malaria attack rates and incidence densities were calculated; transmigrants had a significantly higher rate ( = 0.003) than the Irianese during the low transmission season study (20-weeks long) but not during the high transmission season study (12-weeks long). Lack of exposure-induced immunity left the transmigrants at a minimum 17–25% greater relative risk of becoming parasitemic compared with the Irianese during the low transmission season study. During the high transmission season study, 50% of the transmigrants were positive by week 6 and 50% of the Irianese by week 9. During the low transmission season, 50% of the transmigrants were positive by week 10 and 43% of the Irianese were positive by week 17. Entomologic studies showed that was the predominant vector (> 98% of anopheline catch). Entomologic inoculation rates for were 0.018 and 0.39 infective bites/person/night for the low and high transmission seasons, respectively. New cases represented between 16% and 42% of all initial malaria cases. Factors affecting sample size calculation were evaluated, including causes of loss to follow-up, and sample sizes required to complete the study under several sets of conditions were calculated. The confidence intervals around specific sample sizes were calculated high-lighting the need to determine the sample size based not only on predicted vaccine efficacy and estimated subject attrition but also on a desired width of confidence interval for the observed vaccine efficacy.


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