Candidate Malaria Vaccine Effective for 15 Months in Clinical Trial

Magnified photomicrograph of Plasmodium falciparum parasites that cause malaria, in a growing stage. CDC/Dr. Mae Melvin.Despite global efforts to disrupt malaria transmission using mosquito nets and drug therapies, the disease remains widespread: hundreds of millions of cases occur each year, causing hundreds of thousands of deaths. While these measures can help to control the disease, an effective vaccine against malaria would be a major contribution to global public health.

The leading candidate vaccine against malaria is the RTS,S vaccine, which is currently in Phase III trials in seven countries in Africa. (Phase III trials are used to confirm the effectiveness of a drug as determined in Phase II trials, as well as to continue monitoring the drug for safety.) While this vaccine offers only partial protection against malaria—prior data showed it to be 53% effective eight months after vaccination—even this level of protection would be a significant improvement to public health efforts.

Recently, researchers studied the length of the protection provided by the vaccine. Two groups of 447 healthy children each (for a total of 894) between 5-17 months of age were randomly given either the candidate malaria vaccine or a rabies vaccine, each in a series of three shots. One group was in Kenya, the other in Tanzania. The group in Tanzania could only be followed for a period of one year*; the group in Kenya was followed for a full 15 months.

At the end of the 15-month period, the RTS,S vaccine was found to be 45.8% effective in preventing malaria among the Kenyan group, suggesting that the efficacy of the vaccine did not significantly wane between the eight-month and the fifteen-month marks. As a result, the researchers concluded that the candidate vaccine provides sustained malaria protection for up to 15 months for young children in areas with endemic malaria.

Given the lack of infrastructure in many areas where malaria is most prevalent, the length of protection provided by potential vaccines against the disease is extremely important. Returning to a doctor’s office each year for a booster shot may be merely inconvenient in industrialized nations like the United States, but it can be difficult or impossible in remote regions of sub-Saharan Africa, where the disease is widespread. If the RTS,S candidate vaccine goes into production after the completion of phase III trials, long-lasting protection will be a major factor in its potential success against malaria.

* The researchers reported that the site in Tanzania “did not have the infrastructure to sustain the extended follow-up.”

Sources and more information

The RTS,S candidate vaccine is a subunit vaccine that is a combination of a malaria parasite surface protein and a hepatitis B surface antigen with immunostimulants. Reach more about subunit vaccines in our Different Types of Vaccines article.

Initial study showing efficacy after eight months: “Efficacy of RTS,S/AS01E vaccine against malaria in children 5 to 17 months of age.” New England Journal of Medicine, December 11, 2008.

Olotu A, Lusingu J, Leach A et al. “Efficacy of RTS,S/AS01E malaria vaccine and exploratory analysis on anti-circumsporozoite antibody titres and protection in children aged 5-17 months in Kenya and Tanzania: a randomized controlled trial.” The Lancet Infectious Diseases, February 1, 2011.

U.S. National Institutes of Health record of trial: “Efficacy of RTS,S/AS01 Vaccine Against Episodes of Malaria Due to P. Falciparum Infection in Children.” Record processed at January 27, 2001.