Results published in the Journal of Infectious Diseases from a controlled human malaria infection study conducted by the Walter Reed Army Institute of Research are encouraging. They further validate the protective effects of the candidate vaccine RTS,S/AS01 (RTS,S) against malaria parasite infection, and they provide new insights into how to improve the vaccine’s efficacy. 

 

The study, in adults in the United States who had never had malaria, demonstrated that a delayed and reduced third dose of RTS,S was associated with higher vaccine efficacy. Results showed approximately 87 percent efficacy against infection three weeks after immunization (compared to 63 percent for the standard monthly full-dose regimen). Adjustments in dose or schedule to optimize the cost or ease of use of vaccines are typical in their life cycle management. Fractional dosing, also known as dose sparing, has been used to make vaccines go further when they’re in short supply and to reduce cost per dose. Normally, the goal is to see if results achieved with full doses can be matched using smaller vaccine doses. However, the results from this study are notable as this within-schedule dose-reduction approach provides the first evidence that less vaccine may actually be more effective. Additional testing is required to determine if the results can definitively be attributed to the reduced dosage.

 

It is important to note that these results come from an early-stage clinical trial, using an alternative dosing regimen that has, to date, only been tested in 30 adults in the United States. Studies in field settings, such as Africa, and in children are needed to determine how these early study results translate to parts of the world and populations most affected by malaria. Such studies will take several years to complete. 

 

GSK and PATH have been involved in the fight against malaria for decades, and an important part of that fight has been our work to develop a malaria vaccine. After 30 years of research and development, including completion of a pivotal Phase III efficacy and safety trial and a positive scientific opinion from the European Medicines Agency, we may be close to introducing the current regimen of RTS,S, in sub-Saharan Africa. The World Health Organization (WHO) has recommended and is coordinating a pilot implementation programme involving approximately 750,000 children that will provide additional information on vaccine safety and impact and how best to deliver a four-dose schedule of RTS,S in a real-world setting. The information and data collected during the pilot programme will be beneficial to RTS,S and to any improvement of RTS,S that might come in the future.

 

We continue to invest in vaccine development, including the life cycle management of RTS,S. Although the results reported in the Journal of Infectious Diseases are promising, the regimen used in this early-stage trial will require additional follow-up and several more years of clinical testing. According to WHO, the current four-dose regimen of the RTS,S vaccine candidate is at least 5 to 10 years ahead of other candidate malaria vaccines. 

 

 

Completed in 2014, the large-scale Phase III trial conducted in sub-Saharan Africa showed that three doses of RTS,S given one month apart to children 5 to 17 months old reduced the number of malaria cases by half over the subsequent year. Efficacy waned over time but was prolonged by a fourth dose of the vaccine. Over four years of follow-up, efficacy against clinical malaria was around 40 percent in children receiving four doses. In the trial, more than 1,700 cases of clinical malaria were averted, on average, per 1,000 children vaccinated, over an average 48 months of follow-up.

 

Read more about RTS,S here.