On guard

Policemen wearing face masks to prevent contagion by the swine flu virus, stand at the entrance of a Government building in Mexico City. The World Health Organization said there was no reason to raise a pandemic flu alert to the highest level as the epidemic had remained steady. But WHO acting Assistant Director General Keiji Fukuda added a note of caution about developments in the southern hemisphere, which is entering into the flu-prone winter season.

April 30, 2009