Fever that follows viral infection is believed to be a defence mechanism of the body. High temperature is thought to harm virus more than the host. However, researchers at the University of Oxford, UK, have discovered that one virus has a chilling effect on the defences of the host.

Vaccinia virus, used to vaccinate people against smallpox, releases a protein that actually brings down the body temperature. When researchers infected mice with large doses of Vaccinia, expecting the animals to become feverish, their temperatures dropped instead, by 1