This year's flu season is off to a killer start — literally. The Centers for Disease Control and Prevention (CDC) reported that rates of hospitalizations and deaths from the virus are higher than what's typically expected for this time of year.
But how does a person die from the flu?
The influenza virus can kill a person in several different ways, Live Science reported in 2016.
For instance, the virus can directly cause death, Dr. Amesh Adalja, a senior scholar at the Johns Hopkins Center for Health Security in Baltimore, told Live Science in 2016. This occurs when the flu virus causes such overwhelming inflammation in a person's lungs that they die due to respiratory failure. Severe damage to the lungs makes it impossible for enough oxygen to pass through the lung tissue into the blood, leading to death. [Flu Shot Facts & Side Effects (Updated for 2017-2018)]
When someone dies directly from the flu, it happens very quickly, Adalja added.
The flu can also kill indirectly, meaning that the virus makes a person more susceptible to other health problems, and these health problems lead to death. For example, getting sick with the flu can make certain groups of people, such as older adults and people with chronic illnesses, more susceptible to bacteria that cause pneumonia, according to the Mayo Clinic. "Pneumonia is the most serious complication" of the flu and can be deadly, the Mayo Clinic says.
When a person with the flu gets pneumonia, the pneumonia is considered a secondary bacterial infection, Adalja said. (Pneumonia can be caused by either a virus or bacteria; in the case of a secondary infection after flu, it is caused by bacteria.) Death from such secondary infections usually occurs about a week or so after the person first got sick, because it takes time for the secondary infection to set in, Adalja said.
The flu can lead to death in other ways as well. People with the flu can experience "multiple organ failure" throughout their body (in order words, multiple organs stop working properly), which can be deadly, Adalja said.
The flu can also trigger other serious complications, including inflammation of the heart, brain or muscle tissues, according to the CDC. Infection can also lead to an extreme, body-wide inflammatory response known as sepsis, which can be life-threatening, the CDC says.
The 2017–2018 flu season has been particularly harsh, partially because the predominant strain of flu that's spreading, H3N2, tends to cause more severe symptoms than other strains, Live Science reported this month. And although the flu strains circulating this year do match up with those covered in the season's flu vaccine, an odd phenomenon may have occurred during the vaccine-making process inside chicken eggs. During that process, flu strains can acquire genetic changes, and this may have happened for the H3N2 component of the vaccine, Adalja said previously.
Originally published on Live Science.