The flu is known to suffer more in winter, but scientists have found no reason for it. To find an explanation, researchers from New York analyze the conditions of infection of the flu. To do this, they have carried out the experiment with guinea pigs. Several avids have been exposed to the flu virus in different conditions of humidity and temperature. Thus it has been detected that the largest number of rockets are contaminated at a temperature of 5ºC and a humidity of 20-35%. These conditions are more frequent in winter than in other times of the year.