Humans around the world have become accustomed to “flu season” and the yearly threat of influenza. But, why does this annual virus still threaten our health and force us to get a vaccine shot each year?

In SciShow’s video, “The Best Way to Fight the Flu,” host Michael Aranda breaks down the science behind flu season and discusses the most effective ways to beat the influenza virus.

Globally, there are actually two flu seasons every year, because northern and southern hemispheres experience winter at different times and influenza virus thrives in cooler temperatures.

“The flu virus does circulate year round, but the number of cases rapidly increases during those peak months,” Aranda explains.

Additionally, influenza mutates every year, which is why annual shots are required. There are also a handful of different types of the virus and each strain demands unique treatment.

In fact, according to Aranda, “flu vaccines are actually developed months before peak season actually starts.” This could potentially result in a biological change in the virus before the vaccine is administered.

Want to know more about the current flu strain and this winter’s influenza vaccine? Watch the video above.

Read more:

Cold vs. Flu Symptoms 2016: How To Tell The Difference Between The Two

Flu Symptoms 2016: Things To Know About Treatment, Recovery Time