Why does one get the flu shot in October when the flu season begins in December?
You need the vaccination prior to the beginning of the flu
season so your body has had time to develop the immunity from the
vaccine before the viruses start to circulate in your area.
Children take longer to develop the immunity than adults.
It is best to get vaccinated as soon as the vaccine is available
to you, which is usually September in the US and March in the
Southern Hemisphere. You can't take it too early to work (since the
immunity lasts a lifetime to those specific viruses in the
vaccine).
In the Northern Hemisphere, the flu season is considered to be
from October through March, although some extend that to say
through May, especially in the colder regions. So the best time to
get the vaccine, if you are an adult, is approximately 3 weeks
prior to October which allows your body time to fully develop the
immunity after the vaccination before the season starts.
In the Southern Hemisphere, the flu season is considered to be
from April through September. Adults would want to have received
the vaccinations there approximately 3 weeks prior to April.
Children under 10 and infants 6 months old and over require a
series of two vaccinations one month apart and it takes them
approximately one month after the second vaccination to achieve the
immunity, since their immune systems are immature. Babies under 6
months old can not be vaccinated.