Comparative evaluation of intensive pulse polio immunization in district Valsad in the year 2007 and 2008.

Sir, India has started Intensive Pulse Polio Immunization (IPPI) since 1995. An important improvement made in IPPI during 1998 was use of Vaccine Vial Monitors (VVM). The VVM is a small square, made of heat sensitive material, placed on an outer colored circle printed on the label of the OPV vial. There are four stages to read the VVM. In stages 1 and 2, the color of the square remains light gray. It changes with exposure to high temperature to gray in stage 3 to match the color of the outer circle, while in stage 4 the color of the square becomes darker than the outer circle color.