The world’s second vaccine against malaria was launched on Monday as Ivory Coast began a routine vaccine program using shots developed by the University of Oxford and the Serum Institute of India.

The introduction of the World Health Organization (WHO)-approved R21 vaccine comes six months after the first malaria vaccine, called RTS,S and developed by British drugmaker GSK, began being administered in a routine program in Cameroon.

Some 15 African countries plan to introduce one of the two malaria vaccines this year with support from the Gavi global vaccine alliance.

Ivory Coast has received a total of 656,600 doses of the Oxford and Serum shot, which will initially vaccinate 250,000 children aged between 0 and 23 months across the West African country. The vaccine has also been approved by Ghana, Nigeria, Burkina Faso and the Central African Republic.

The rollout of a second vaccine is the latest milestone in the global fight against malaria and should help address a problem that emerged well before either of the two shots was launched: demand for them is likely to far outstrip supply for several years.

Experts say having safe and effective malaria vaccines is important to meet demand. The shot is meant to work alongside existing tools — such as bed nets — to combat malaria, which in Africa kills nearly half a million children under the age of five each year.

The Serum Institute of India, which manufactures the vaccine, has produced 25 million doses for the initial rollout of the shot and “is committed to scaling up to 100 million doses annually,” the company said on Monday about the launch in Ivory Coast.

Serum said it is offering the vaccine for less than $4 per dose, in keeping with its aim to deliver low-cost vaccines at scale.

Results from a large trial in February showed the vaccine prevented around three-quarters of symptomatic malaria cases in young children the first year after they got the shots.

Experts told Reuters at that time that comparing the two malaria vaccines head-to-head was difficult because of the many variables involved in the trials, but overall their performance was similar — a conclusion endorsed by WHO.