Experimental infection and protection against ... - TI Pharma

202 Chapter 10
Figure 3. Mean number of adverse events per volunteer. Data from controls in black
(n=5), volunteers that showed delayed patency in red (n=2) and protected volunteers in
green (n=4). Only adverse events possibly or probably related to malaria are included.
Results
All ten volunteers previously immunised and protected against an experimental
malaria infection, were contacted 32 months after the first immunisation [9]. Six
of these volunteers passed screening for eligibility and were included in the
current follow-up study. Three out of four excluded volunteers were unavailable
and one had to be excluded because of a family history of myocardial infarction
(second degree relative under 55 years of age). Five healthy volunteers were
newly recruited as a control group. Figure 2 shows the trial profile. Eleven
volunteers were challenged by the bites of five Pf-infected mosquitoes and all
completed follow-up. The average age of participating volunteers was 23.6 years
(range 21-28 years old), of whom four were male. Four controls and one
immunised volunteer had previously (range 6 months to 9 years) travelled in
malaria endemic areas during which time they all used malaria prophylaxis, none
of the volunteers was a previous resident of a malaria endemic area. None of
the volunteers reported having used antimalarials within the past 6 months and
none showed positive serology for Pf.
When re-challenged according to the standard protocol by bites of five infected
mosquitoes, four out of six of the immunised volunteers never developed bloodstage
parasitemia by microscopy during daily follow-up. One of these volunteers
requested presumptive treatment with anti-malarials on day 14 post-infection
for reasons unrelated to the trial. The remaining two volunteers showed a
markedly delayed patent parasitemia on days 15 and 18, respectively.