Flu season is an annually recurring period characterized by the prevalence of outbreaks of influenza (flu). The season occurs during the cold half of the year in each hemisphere. Influenza activity can sometimes be predicted.
While the beginning of major flu activity in each season varies by location, in any specific location these minor epidemics usually take about three weeks to peak, and another 3 weeks to significantly diminish. In the United States, the flu season is considered October through May.
An influenza pandemic is an epidemic of an influenza virus that spreads on a worldwide scale and infects a large proportion of the world population. In contrast to the regular seasonal epidemics of influenza, these pandemics occur irregularly – there have been about nine influenza pandemics during the last 300 years. Pandemics can cause a high level of mortality. For example, the 1918 Spanish flu pandemic - the worst in recorded history, was estimated to be responsible for the deaths of approximately 50–100 million people.
Influenza pandemics occur when a new strain of the influenza virus is transmitted to humans from another animal species. Species that are thought to be important in the emergence of new human strains are pigs, chickens and ducks.
These novel strains are unaffected by any immunity people may have to older strains of human influenza and can therefore spread extremely rapidly and infect very large numbers of people.
According to an estimate by the Centers for Disease Control and Prevention (CDC), there were:
* approximately 45 million cases of the flu in the United States
resulting in an estimated 810,000 flu-associated hospitalizations
* estimated 61,000 flu-associated deaths.
Flu killed and hospitalized more people in the United States in 2017-2018 than any seasonal influenza in decades. It sickened millions of people as overwhelmed hospitals pitched tents to treat patients.
* estimated 29 million flu cases in the United States
* 497,000 flu-related hospitalizations
* 38,000 flu-related deaths
* estimated 34 million Americans got the flu
* 710,000 were hospitalized
* about 56,000 died
* 22,048 flu cases were reported through the end of 2012.
By the same time the previous year, only 849 flu cases had been reported
This flu season seemed especially bad. Boston declared a public health emergency and a Pennsylvania hospital was forced to construct a tent to handle flu cases.
2009 swine flu pandemic
* lasted from January 2009 to August 2010
* was the second of the two pandemics involving H1N1 influenza virus (the first being the 1918–1920 Spanish flu pandemic)
* estimated 1.4 billion people worldwide contracted the illness – more than the number of people infected by the Spanish flu pandemic
* about 150,000–575,000 fatalities
A follow-up study done in September 2010 showed that the risk of serious illness resulting from the 2009 H1N1 flu was no higher than that of the yearly seasonal flu.
How Is Pandemic Flu Different from Seasonal Flu?
Corona Virus Pandemic Update by country