A follow-up to the landmark six-month efficacy study results published by The Lancet in 2004, today's findings show that RTS,S/AS02A remained efficacious over an 18-month observation period.

The findings are published in the November 15, 2005 on-line edition of The Lancet and are presented at the Multilateral Initiative on Malaria's Pan-African Malaria Conference in Yaounde, Cameroon.

CISM conducted the study in partnership with Mozambique's Ministry of Health. Fourteen hundred forty-two children who had received a three-dose regimen of the vaccine in 2003 were followed for continued assessment of safety, immunogenicity, and efficacy. No further malaria vaccinations were given. For the 18-month period of follow-up, RTS,S/AS02A was shown to reduce clinical malaria episodes by 35 percent and severe malaria episodes by 49 percent.

"These results answer an essential question remaining from the release of the six-month efficacy data a year ago," said Pedro Alonso, M.D., Ph.D., lead author of the Lancet article, scientific director of CISM, and head of the Center for International Health at the Hospital Clinic of the University of Barcelona.

"The unprecedented response demonstrated in this study is further evidence that an effective vaccine to help control the malaria pandemic, which kills more than one million people a year in developing countries, is very possible."

"Several more years of clinical investigation will be needed before this vaccine is ready for licensure and implementation, but today's results move us an important step closer to developing a vaccine that can provide lasting protection to help save millions of lives," said Jean Stephenne, President of GSK Biologicals, which has been working on the development of this vaccine for more than 15 years. "The world should now take all required actions in order to get this vaccine to all who need it."

The immunogenicity and safety profiles of the vaccine remained promising. In addition, children vaccinated with RTS,S/AS02A were found at the end of the follow-up period to be 29 percent less likely to be infected with the Plasmodium falciparum malaria parasite.

The participants in the current study will continue to be followed, and MVI and GSK--with CISM and other clinical trial partners in Africa--will continue clinical development of the RTS,S/AS02A vaccine. In October, the Bill & Melinda Gates Foundation announced a $107.6 million grant to MVI to support this work.

"The ability of this vaccine to protect children from severe malaria for at least 18 months makes it a very promising potential public health tool for the developing world," said Dr. Melinda Moree, PhD, director of MVI, a global program created to overcome barriers to malaria vaccine development. "We are committed to making an affordable, safe, and effective malaria vaccine available as quickly as possible to those who need it most."

The reported results are from the single-blind follow-up phase of a randomized, double-blind, controlled proof of concept study in children one to four years of age. The RTS,S/AS02A vaccine candidate uses a recombinant protein that fuses a part of the Plasmodium falciparum circumsporozoite protein with the hepatitis B surface antigen and targets immune responses against the stage injected by mosquitoes.

Early development of this candidate was undertaken by GSK in close collaboration with the Walter Reed Army Institute of Research. In January 2001, GSK Biologicals and MVI entered into an agreement to develop the vaccine for children in developing countries. PATH launched MVI in 1999 with a grant from the Bill & Melinda Gates Foundation.

Today's announcement highlights GSK's commitment to working to develop both preventative vaccines and new therapies to treat malaria. In addition to this announcement on the extended efficacy of the RTS,S vaccine candidate, GSK also today announced clinical results affirming that a new artemisinin-based combination therapy, CDA (chlorproguanil hydrochloride-dapsone-artesunate), may be effective against drug-resistant malaria.

CDA is being developed in collaboration with the Medicines for Malaria Venture, the World Health Organisation's Special Programme for Research and Training in Tropical Diseases, and academic partners at the University of Liverpool, Liverpool School of Tropical Medicine and the London School of Hygiene & Tropical Medicine.

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