August 19, 2014
By Will Boggs MD
NEW YORK - The RTS,S/AS01 malaria vaccine retains efficacy after 18 months in children and young infants, according to results from 11 sites in 7 countries across Africa.
"Currently there is no vaccine against malaria," Dr. Mary J. Hamel from the Centers for Disease Control and Prevention Malaria Branch in Atlanta, Georgia told Reuters Health.
"We are making progress in the fight against malaria, and malaria is decreasing as insecticide treated nets and artemisinin combination therapy are scaled up across Africa," she added - but the disease still kills more than 600,000 people per year, mostly young African children.
The new data are from an ongoing phase III trial.
In an earlier paper, the researchers, including Dr. Hamel, reported that vaccine efficacy against the first or only episode of clinical malaria was 56% in children aged 5 to 17 months at the time of their first vaccination and 31% in infants first vaccinated at age 6 to 12 weeks.
Now, in a report online July 29th in PLoS Medicine, they report vaccine efficacy results in these same groups at 18 months, just before the planned administration of a booster dose of RTS,S/AS01.
The study included 8923 children and 6537 young infants, of whom 6885 (77%) children and 6003 (92%) young infants were included in the per-protocol population.
During the 18 months of follow-up, the incidence of all episodes of malaria among children was significantly lower in the per-protocol group (0.69/person-year) than in the control group (1.17/person-year), for an overall vaccine efficacy of 46%. Vaccine efficacy varied widely across sites, ranging from 40% to 77%.
The reduction in the incidence of clinical malaria declined steadily from 68% during months 1-6 to 41% during months 7-12 and 26% during months 13-18 after vaccine dose 3.
Through the 18 months, vaccine efficacy among children was 31% against prevalent parasitemia, 36% against severe malaria, 42% against malaria hospitalization, and 19% against all-cause hospitalization.
The researchers estimate that malaria vaccination prevented an average of 829 cases of clinical malaria, 18 cases of severe malaria, 43 malaria hospitalizations, and 52 all-cause hospitalizations per 1000 children vaccinated with RTS,S/AS01.
Results were less impressive for young infants, whose vaccine efficacy for all episodes of clinical malaria during the 18 months was 27%. The reduction in clinical malaria incidence fell steadily from 47% in the first 6 months to 23% in the second six months and 12% in the last six months.
Still, use of the vaccine prevented an estimated 449 cases of clinical malaria and six cases of severe malaria per 1000 young infants vaccinated.
Serious adverse events were less common in children vaccinated with RTS,S/AS01 than in control children, whereas there was no difference in severe adverse event frequency between vaccinated and control young infants.
"The final results of this trial, in which children vaccinated at 5-17 months of age and young infants vaccinated at 6-12 weeks of age were followed for up to 4½ years, will be available early next year," Dr. Hamel said. "Those results will include the long term safety analysis and information on the duration of protection and whether the booster dose, given after 18 months follow-up, is able to restore or enhance vaccine efficacy. These results will be key in determining the role of this vaccine for public health use."
"The European Medicines Agency will review the regulatory packet submitted by GSK later this year and the World Health Organization will review the information early next year," Dr. Hamel said. "If the opinion from the EMA is favorable, and if WHO recommends the vaccine for use, the vaccine will then be available for licensure and use in African countries. Should that happen, RTS,S/AS01 would be the first malaria vaccine available for use."
GlaxoSmithKline Biologicals SA (GSK) sponsored the trial, and both GSK and PATH Malaria Vaccine Initiative funded the study.
PLoS Medicine 2014.
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