Here he developed his interests in malaria and epidemic meningitis, both infections whose epidemiology is strongly influenced by the climate of the African Sahel and sub-Sahel. During his time in Zaria, he conducted some of the first trials of meningococcal polysaccharide vaccines and demonstrated the ability of a single injection of a long-acting chloramphenicol preparation to treat cases of meningococcal meningitis successfully during epidemics when clinical facilities could be overwhelmed.

He and his colleagues showed that because of the seasonal nature on malaria transmission in The Gambia and other countries of the African Sahel and sub-Sahel, administering antimalarial drugs to young children prophylactically during just a few months of the year could reduce mortality and morbidity in young children. Members of the malaria team also demonstrated the efficacy of intravenous artesunate in children with severe malaria and undertook one of the first trials of artemisinin combination therapy including the first trial of artemether-lumefantrine, now the most widely used treatment for malaria in Africa.