Influenza

Influenza (or as it is commonly known, the flu or the grippe) is a contagious disease, caused by an RNA virus of the orthomyxoviridae family. It rapidly spreads around the world in seasonal epidemics, imposing considerable economic burden, in the form of health care costs and lost productivity. Major genetic changes in the virus have caused three influenza pandemics in the 20th century, killing millions of people. The name comes from the old medical belief that unfavourable astrological influences cause the disease.

Flu season

Influenza reaches peak prevalence in winter, and because the Northern and Southern Hemisphere have winter at different times of the year, there are actually two flu seasons each year. Hope-Simpson (1981) observed that influenza outbreaks are globally ubiquitous, and consistently occur six months following the time of maximum solar radiation in an area. Therefore, the World Health Organization makes two vaccine formulations every year; one for the Northern, and one for the Southern Hemisphere.

Related Topics:
Winter - Northern - Southern Hemisphere - World Health Organization - Vaccine

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

While most influenza outbreaks in the Northern Hemisphere tend to peak in January or February, not all do. For example, the influenza pandemic of 1918 and 1919 reached peak virulence during late spring and summer worldwide, and not until October in the US. It remains unclear why outbreaks of the flu occur seasonally rather than uniformly throughout the year. One possible explanation is that, because people are indoors more often during the winter, they are in close contact more often, and this is enough to trigger the outbreak. Another is that the cold weakens the immune system; however, the virus is contracted in a warm indoor environment in which it can thrive.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~