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Results from a phase 2 study of the malaria vaccine RTS,S (also known as RTS,S/AS01 or Mosquirix) suggest its efficacy decreases over time, and this decline is fastest in children living in areas with higher-than-average rates of malaria.
Researchers say the results suggest the benefits of the vaccine are likely to vary across different populations and highlight the need for more research to
determine the most effective way of using RTS,S, which last year became the first malaria vaccine to receive a green light from the European Medicines Agency.
“We found that 3-dose vaccination with RTS,S was initially protective, but this was offset by a rebound in later years among children exposed to higher-than-average levels of malaria-carrying mosquitoes,” said Philip Bejon, PhD, of the Kenya Medical Research Institute–Wellcome Trust Programme in Kilifi, Kenya.
Dr Bejon and his colleagues reported these results in NEJM.
The researchers followed 447 children who had received 3 doses of either RTS,S or a rabies (control) vaccine when they were 5 months to 17 months old.
After 7 years, there were 312 children still involved in the study. During the first year, the risk of getting malaria in the vaccinated children was 35.9% less than in the control group. After 7 years, this protection fell to 3.6%.
And in children exposed to higher-than-average rates of malaria, there were slightly more cases of malaria in the vaccinated group than the control group—1002 and 992 cases, respectively—5 years after vaccination.
This “rebound” effect, which has been seen in previous studies, is thought to occur because children initially protected by the vaccine develop their natural immunity against malaria more slowly than unvaccinated children.
Results from a phase 3 study showed that 3 doses of RTS,S reduced the risk of malaria in young children by 28% over 4 years, but this improved to 36% when children were given a fourth dose 18 months after the first dose. Longer-term follow up of these children is ongoing.
“Overall, our study shows that RTS,S can benefit children but suggests that a fourth dose may be important for sustaining this protection over the long term and to protect against a potential rebound,” said Ally Olotu, PhD, of the Kenya Medical Research Institute–Wellcome Trust Programme.
“Results from 3 sites involved in the original phase 3 study that are continuing follow up, and the WHO’s planned pilot program, will tell us more about the vaccine’s efficacy in different settings and help determine which populations would benefit most from receiving it as part of a wider vaccination strategy.” 
Photo by Caitlin Kleiboer
Results from a phase 2 study of the malaria vaccine RTS,S (also known as RTS,S/AS01 or Mosquirix) suggest its efficacy decreases over time, and this decline is fastest in children living in areas with higher-than-average rates of malaria.
Researchers say the results suggest the benefits of the vaccine are likely to vary across different populations and highlight the need for more research to
determine the most effective way of using RTS,S, which last year became the first malaria vaccine to receive a green light from the European Medicines Agency.
“We found that 3-dose vaccination with RTS,S was initially protective, but this was offset by a rebound in later years among children exposed to higher-than-average levels of malaria-carrying mosquitoes,” said Philip Bejon, PhD, of the Kenya Medical Research Institute–Wellcome Trust Programme in Kilifi, Kenya.
Dr Bejon and his colleagues reported these results in NEJM.
The researchers followed 447 children who had received 3 doses of either RTS,S or a rabies (control) vaccine when they were 5 months to 17 months old.
After 7 years, there were 312 children still involved in the study. During the first year, the risk of getting malaria in the vaccinated children was 35.9% less than in the control group. After 7 years, this protection fell to 3.6%.
And in children exposed to higher-than-average rates of malaria, there were slightly more cases of malaria in the vaccinated group than the control group—1002 and 992 cases, respectively—5 years after vaccination.
This “rebound” effect, which has been seen in previous studies, is thought to occur because children initially protected by the vaccine develop their natural immunity against malaria more slowly than unvaccinated children.
Results from a phase 3 study showed that 3 doses of RTS,S reduced the risk of malaria in young children by 28% over 4 years, but this improved to 36% when children were given a fourth dose 18 months after the first dose. Longer-term follow up of these children is ongoing.
“Overall, our study shows that RTS,S can benefit children but suggests that a fourth dose may be important for sustaining this protection over the long term and to protect against a potential rebound,” said Ally Olotu, PhD, of the Kenya Medical Research Institute–Wellcome Trust Programme.
“Results from 3 sites involved in the original phase 3 study that are continuing follow up, and the WHO’s planned pilot program, will tell us more about the vaccine’s efficacy in different settings and help determine which populations would benefit most from receiving it as part of a wider vaccination strategy.”
Photo by Caitlin Kleiboer
Results from a phase 2 study of the malaria vaccine RTS,S (also known as RTS,S/AS01 or Mosquirix) suggest its efficacy decreases over time, and this decline is fastest in children living in areas with higher-than-average rates of malaria.
Researchers say the results suggest the benefits of the vaccine are likely to vary across different populations and highlight the need for more research to
determine the most effective way of using RTS,S, which last year became the first malaria vaccine to receive a green light from the European Medicines Agency.
“We found that 3-dose vaccination with RTS,S was initially protective, but this was offset by a rebound in later years among children exposed to higher-than-average levels of malaria-carrying mosquitoes,” said Philip Bejon, PhD, of the Kenya Medical Research Institute–Wellcome Trust Programme in Kilifi, Kenya.
Dr Bejon and his colleagues reported these results in NEJM.
The researchers followed 447 children who had received 3 doses of either RTS,S or a rabies (control) vaccine when they were 5 months to 17 months old.
After 7 years, there were 312 children still involved in the study. During the first year, the risk of getting malaria in the vaccinated children was 35.9% less than in the control group. After 7 years, this protection fell to 3.6%.
And in children exposed to higher-than-average rates of malaria, there were slightly more cases of malaria in the vaccinated group than the control group—1002 and 992 cases, respectively—5 years after vaccination.
This “rebound” effect, which has been seen in previous studies, is thought to occur because children initially protected by the vaccine develop their natural immunity against malaria more slowly than unvaccinated children.
Results from a phase 3 study showed that 3 doses of RTS,S reduced the risk of malaria in young children by 28% over 4 years, but this improved to 36% when children were given a fourth dose 18 months after the first dose. Longer-term follow up of these children is ongoing.
“Overall, our study shows that RTS,S can benefit children but suggests that a fourth dose may be important for sustaining this protection over the long term and to protect against a potential rebound,” said Ally Olotu, PhD, of the Kenya Medical Research Institute–Wellcome Trust Programme.
“Results from 3 sites involved in the original phase 3 study that are continuing follow up, and the WHO’s planned pilot program, will tell us more about the vaccine’s efficacy in different settings and help determine which populations would benefit most from receiving it as part of a wider vaccination strategy.”