Flu

The flu is a sickness caused by a virus called influenza. It mainly attacks the nose, throat, and lungs. The flu spreads from person to person, often during the colder months of the year. Most people who get the flu feel better in about a week or two. But the flu can be serious, and it kills hundreds of thousands of people around the world each year.

The flu and the common cold can feel similar, but they are not the same. A cold usually comes on slowly and stays mild. The flu hits hard and fast. People with the flu often run a high fever, ache all over, feel very tired, and cough a lot. Many also get a sore throat, a runny nose, or a headache. Kids sometimes throw up too, though grown-ups usually do not.

Flu spreads through tiny drops in the air. When a sick person coughs, sneezes, or even talks, those drops carry the virus. If another person breathes them in, or touches a surface where they landed and then touches their own face, the virus can get into their body. From there it sneaks into cells in the nose and throat and starts making copies of itself.

Once the virus is inside, the immune system fights back. The fever, the runny nose, and the tiredness are not really caused by the virus. They are caused by the body's defense team working hard. Resting, drinking water, and eating gentle foods give the immune system the energy it needs to win.

There are many kinds of flu virus, and they change a little bit every year. That is why a flu shot you got last winter may not protect you this winter. Scientists watch the flu around the world and update the vaccine each year to match the kinds they expect to spread. The flu shot is the best tool we have to stop the flu from getting bad.

Sometimes a brand new kind of flu appears that almost no one has fought before. When that happens, the flu can spread across the whole world. This is called a pandemic. The worst one in modern history was the 1918 flu pandemic, which infected about a third of all people on Earth and killed at least 50 million of them. Doctors today watch closely for warning signs, hoping to catch the next big flu early.