In the last 6 weeks, 84 children have been announced dead due to the the flu.

With flu related hospitalizations rising to nearly 68 out of every 100,000 people in the U.S. this week, the Center for Disease Control (CDC) officially marks this flu season in the U.S. as an epidemic. With the hospitalization rate up to 10.1%, this years flu season is the deadliest since the 2009 swine flu pandemic.

The “flu season” is caused by the spread of an acute viral infection called the influenza virus. The virus can spread worldwide and infect people of any age group. The virus affects about 3-5 million people worldwide, 80% of which are 65 years or older according to The World Health Organization (WHO). While people in this age group are more susceptible to the virus, children, pregnant women, and those who are already ill are more vulnerable as well.

When understanding the flu, it is important to recognize how it spreads and what causes it. The virus spreads through tiny drops of saliva that can become airborne when someone with the virus sneezes or coughs. The flu can also be passed through direct contact like kissing or touching, according to Harvard Health. Popular Science gives several theories as to why flu sickness rates rise during the winter months, such as longer times spent indoors.

People may not recognize that they have the flu, as symptoms take up to two weeks to develop after it has entered the body, according to the CDC. After symptoms have begun, the flu can stay in one’s system for another 7-10 days according to Harvard Health.  

The flu is often characterized by fever, aches, pains, a sore throat, or a cough. That being said, the deadly nature of the virus does not come from the virus itself, but rather how it renders the person vulnerable to other diseases.

Most deaths are caused by an overwhelming bodily response to the virus in which the body sends cytokine proteins to the area to create an inflammatory response. The inflammation, which typically occurs within the lungs, allows the air sacs (alveoli) of the lungs to fill up with fluid, leading to bacterial infections. Sepsis, or the presence of bacteria in bodily tissues, often allows deadly diseases like pneumonia to enter the bloodstream and spread to other areas of the body.

There are things one can do to protect against the virus, though. Starting in October, flu vaccines have become available to the public. The vaccines are created by various groups of researchers in conjunction with WHO.

Twice a year, the WHO comes together to discuss virus vaccinations for the northern and southern hemispheres. They then make specific reports about what strains of the influenza virus they predict will spread, and how to most effectively protect against it. Each country, however, makes the decision on whether or not to reproduce the vaccine.

The flu vaccine is the most recommended and most effective way to protect against the virus according to the CDC. Though flu activity seems to be declining, flu season will not officially end for another few weeks.