Use of fractional dose tetravalent A, C, W135 and Y meningococcal polysaccharide vaccine: A non inferiority trial by Guerin, P, Naess, L, Fogg, C, Rosenqvist, E, Pinoges, L, Bajunirwe, F, Twesigye, R, Borrow, R, Froholm, O, Batwala, V, Aaberge, I, Rottingen, J, Piola, P, Caugant, D