MALARIA VACCINE STUDY SITE IN IRIAN-JAYA, INDONESIA - PLASMODIUM-FALCIPARUM INCIDENCE MEASUREMENTS AND EPIDEMIOLOGIC CONSIDERATIONS IN SAMPLE-SIZE ESTIMATION
Tr. Jones et al., MALARIA VACCINE STUDY SITE IN IRIAN-JAYA, INDONESIA - PLASMODIUM-FALCIPARUM INCIDENCE MEASUREMENTS AND EPIDEMIOLOGIC CONSIDERATIONS IN SAMPLE-SIZE ESTIMATION, The American journal of tropical medicine and hygiene, 50(2), 1994, pp. 210-218
Citations number
14
Categorie Soggetti
Public, Environmental & Occupation Heath","Tropical Medicine
Malaria epidemiologic and entomologic studies were performed during bo
th the high transmission and low transmission seasons to characterize
the Plasmodium falciparum malaria transmission at a proposed malaria v
accine trial site in Irian Jaya, Indonesia. The study population consi
sted of two subsets: native Irianese men with lifelong exposure to mal
aria and transmigrants who arrived from a nonmalarious area 2.5 years
before the start of the study. All subjects received a radical cure fo
r malaria and were then monitored weekly by blood film. Both P. falcip
arum malaria attack rates and incidence densities were calculated; tra
nsmigrants had a significantly higher rate (P = 0.003) than the Iriane
se during the low transmission season study (20-weeks long) but not du
ring the high transmission season study (12-weeks long). Lack of expos
ure-induced immunity left the transmigrants at a minimum 17-25% greate
r relative risk of becoming parasitemic compared with the Irianese dur
ing the low transmission season study. During the high transmission se
ason study, 50% of the transmigrants were P. falciparum positive by we
ek 6 and 50% of the Irianese by week 9. During the low transmission se
ason, 50% of the transmigrants were positive by week 10 and 43% of the
Irianese were positive by week 17. Entomologic studies showed that An
opheles koliensis was the predominant vector (> 98% of anopheline catc
h). Entomologic inoculation rates for P. falciparum were 0.018 and 0.3
9 infective bites/person/night for the low and high transmission seaso
ns, respectively. New P. vivax cases represented between 16% and 42% o
f all initial malaria cases. Factors affecting sample size calculation
were evaluated, including causes of loss to follow-up, and sample siz
es required to complete the study under several sets of conditions wer
e calculated. The confidence intervals around specific sample sizes we
re calculated highlighting the need to determine the sample size based
not only on predicted vaccine efficacy and estimated subject attritio
n but also on a desired width of confidence interval for the observed
vaccine efficacy.