Prices are subject to supply side shocks which can drive inflation up well above policy targets, as happened in 2011. Monetary policy cannot realistically prevent inflation from rising in the short term if prices have been hit by a large supply shock, such as a food price shock, in Uganda or anywhere else in the world.
What monetary policy can realistically achieve is to bring core inflation back down over a period of time, which in most cases will probably be in the region of a year at least, depending on the size and nature of the shock.