A virus that causes the common cold may be saving people from swine flu. If this intriguing idea turns out to be true, it would explain why swine flu's autumn wave has been slow to take off in some countries and point to new ways to fight flu.
"It is really surprising that there has not been more pandemic flu activity in many European countries," says Arnold Monto, an epidemiologist at the University of Michigan, Ann Arbor.
In France, flu cases rose in early September, then stayed at about 160 per 100,000 people until late October, when numbers started rising again. The delayed rise was puzzling, says Jean-Sebastien Casalegno of the French national flu lab at the University of Lyon.
He reports that the percentage of throat swabs from French respiratory illnesses that tested positive for swine flu fell in September, while at the same time rhinovirus, which causes colds, rose (Eurosurveillance, vol 14, p 19390). He told New Scientist that in late October, rhinovirus fell - at the same time as flu rose. He suspects rhinovirus may have blocked the spread of swine flu via a process called viral interference.