A large-scale pilot of what has been called the world's first malaria vaccine to give partial protection to children has begun in Malawi.
The RTS,S vaccine trains the immune system to attack the malaria parasite, which is spread by mosquito bites.
Earlier, smaller trials showed that nearly 40% of the 5-to-17-month-olds who received it were protected.
Malaria cases appear to be on the rise again after a decade of success in combating the deadly disease.
"This is a landmark moment for immunisations, malaria control, and public health," Dr Kate O'Brien, Director of Immunisation and Vaccines at the World Health Organization, told the BBC.
According to the most recent annual figures, global malaria cases are no longer falling, sparking concerns about its resurgence.
Malawi is the first of three countries chosen for the pilot to roll out the vaccine. It aims to immunise 120,000 children aged two years and below. The other two countries, Ghana and Kenya, will introduce the vaccine in the coming weeks.
The three countries were picked because they already run large programmes to tackle malaria, including the use of bed nets, yet still have high numbers of cases.
Malaria kills some 435,000 people around the world each year, the majority of them children. Most of these deaths are in Africa, where more than 250,000 children die every year, according to the World Health Organization (WHO).
BDST: 1901 HRS, APR 23, 2019