What Exactly Happens to Your Body When You Get Flu?

Health officials estimate almost 10 million people have already fallen sick this flu season, and 4,800 have died. But what exactly happens to the body when you come down with the virus?

In order to take hold, influenza must first enter the body. The viruses that cause the sickness are thought to travel on droplets of liquid, which are launched into the air when an infected person coughs, sneezes, or talks. These land in the mouths and or noses of others, even if they're up to 6 feet away. In rare cases, the flu can be passed on if a person touches a surface contaminated with the virus, and then touches their mouth, nose or eyes.

From there, the virus enters the respiratory system and sticks to cells lining the airways. Once inside the cells, it replicates and matures, Libby Richards, associate professor at the Purdue School of Nursing, Indiana, told Newsweek. Next, the virus exits the cell and invades others, triggering an immune response. This complex system of chemical defences is what leads to many of the flu symptoms, she said.

Unlike cold viruses, which tend to only infect the upper airways of the nose, throat and sinuses, Richards said the flu targets both the upper and lower airways—including the lungs. That's why people sick with the flu often feel worse than those with a common cold.

The infection can also lead to inflammation across the body, which is why it can cause complications like pneumonia, as well as problems with the heart, brain, and muscles.

The symptoms, which often come on suddenly according to health officials, include a fever, cough, sore throat, and a runny nose. Sufferers may also experience aches and pain in the muscles, headaches, and fatigue. Vomitting and diarrhea can also occur, although this is more common in children.

As the lungs can be involved in the flu infection, it can be harder for the body to oxygenate blood, said Richards.

The way the symptoms manifest in the body partly comes down to a person's health status, said Richards. Things such as an individual's age, their history of other infections, genetics, and lifestyle factors—including whether they smoke—can impact their immune response, as well as the virulence of the virus, or its ability to damage its host.

Most people who get the flu will endure unpleasant but relatively mild symptoms, and will get better on their own in less than two weeks. However, some people are more likely to suffer complications that need hospital treatment, and can even be deadly, the U.S. Centers for Disease Control and Prevention (CDC) warns. Those include young children, kids with neurologic conditions, people aged 65 and over, diabetics and pregnant women. Individuals with HIV/AIDs, cancer, and cardiovascular problems are also at a higher risk.

One of the best ways to prevent the flu is to get vaccinated against the season's strain. This year, some 171.7 million doses have be distributed, according to the CDC.

"It definitely is not too late to get vaccinated," stressed Richards. "We are currently in the height of flu season and we likely are not at the peak yet, meaning we are likely to see the number of flu cases continue to rise. Most often flu season peaks in February. So it is very likely that we will be seeing many more cases of the flu into March and maybe April.

"Getting the flu vaccine isn't just about individual health, it's about family and community health. High rates of flu vaccination reduces the chance the virus can spread and protects those who are unable to be vaccinated such as babies less than 6 months old," she said.

"While one person may only be mildly impacted if they get the flu—they could spread the flu to others who could be severely impacted. Because we can't predict how people will react if they get sick, getting the flu shot is the best prevention strategy."

Second to being vaccinated, washing your hands frequently is the next best way to keep the bug at bay, said Richards, in addition to taking steps to keep your immune system strong. Getting between seven to nine hours sleep, staying a healthy weight, drinking nine to 12 cups of "good" fluids "maybe not caffeine and sugar laden beverages," and hitting the minimum exercise guidelines can all help, she suggested. "Don't smoke and limit alcohol consumption," said Richards, adding: "When possible, try to limit stress."

It is also wise to avoid touching your mouth, nose, and eyes to stop the virus from entering the body through the mucous membranes, Richards advised, and stay away from crowds when possible.

As the flu virus can survive on hard surfaces for 24 hours, wiping down surfaces that are frequently touched—like remote controls, phones, toys, and door hands— with a disinfectant wipes is also helpful.

"Think about how many people touch grocery carts or door knobs in that period of time," said Richards.

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A stock image shows a sick woman blowing her nose. Getty