His 1943 handbook on malaria control, "Malaria in the South Pacific", became a standard text. As a specialist in tropical diseases (malaria, dengue fever, sand-fly fever and dysentery) his work contributed to minimising deaths in the New Zealand army. The pre-war experience and malaria records of Sayers was also helpful to the United States forces in reducing malaria rates during the Solomon Islands campaign. His contribution was acknowledged by the award of the Legion of Merit by the United States.