MEASLES vaccine comes in powder form. It must be used immediately after it is mixed with a fluid, says Dr Jacob John, former professor of the Department of Clinical Microbiology and Virology . Multi-vial doses of these vaccines must be used within four hours; else they will act as a medium for growing bacteria that can secrete toxins, he says. Dr John recalled that in 1978, a child was reported dead in Salem due to the administration of measles vaccine. As a member of the investigation team, he found out that it was a case of peculiar toxins developed by Staphylococcus Aurous, a bacterium normally found on the human skin, multiplied manifold while secreting a group of toxins that could cause complications, including death. In 1980, six children died after they administered vaccines in Tamil Nadu and in Cuddappah in Andhra Pradesh. A probe panel attributed the deaths to Toxic Shock Syndrome (TSS) caused by the same group of bacteria. Dr John suspects that the incident in Tiruvallur district could be a case of TSS, but adds that it must be thoroughly investigated.