Influenza or the flu is a contagious, viral infection that attacks your nose, throat and lungs. It can cause fever, chills, runny nose, sore throat, cough, muscle aches and fatigue.

The flu virus is extremely small and only visible through electron microscopes. Inside the virus, genetic material contains the information to make more copies of the same virus. A protein shell provides a hard protective enclosure for the genetic material as the virus travels between the people or animals it infects. An outer envelope allows the virus to infect cells by merging with the cell’s outer membrane. Projecting from the envelope are spikes of protein molecules.

The flu virus uses its H-spikes like a key to get inside your cells. N-spikes allow copies of the virus to break away from your infected cells to infect more cells. There are 17 known types of H-spikes and 9 types of N-spikes that scientists use to name different flu viruses, such as the virus H5N1.

You get the flu by touching an object that has the flu virus on it, or through exposure to body fluids from people or animals infected with the virus. When an infected person talks, coughs or sneezes, droplets carrying the influenza virus may land in your mouth or nose and then move into your lungs. Once inside your body, the influenza virus comes into contact with the cells in your nose, throat or lungs. The H-spike on the virus inserts into a receptor molecule on your healthy cell membrane like a key in a lock. This action allows the virus to get inside your cell. Next, the virus travels inside a sac made from your cell membrane to your cell’s nucleus. Then the viral envelope and cell membrane sac combine, allowing the viral genetic material to leave the sac and enter the nucleus.

The viral genetic material hijacks the energy and materials in your cell’s nucleus to make thousands of copies of itself. Some of the genetic material moves out of the nucleus, then attaches to ribosomes, which are the protein building part of your cell. Ribosomes use information from the genetic material to make other viral proteins, such as the H- and N-spikes.

A packaging structure in your cell called the Golgi apparatus carries the H- and N-spikes in vesicles, which merge with your cell’s membrane. All the parts needed to create a new virus gather just beneath your cell’s membrane.

Then a new virus begins to bud off from the cell membrane. During this process, the newly-created virus gets stuck on your cell’s membrane when a viral H-spike locks on to membrane receptors. However, the virus has a way to get around this problem. The viral N-spike frees the virus by cutting it away from the receptor. New influenza viruses are now free to infect more of your cells, and cause you to develop the flu.

If you have the flu, your doctor may prescribe Oseltamivir which you would take orally, or Zanamivir which you would take using an inhaler to help speed your recovery or reduce your risk for complications. These antiviral drugs stop the influenza virus by blocking the viral N-spike from freeing the virus. This causes the new viruses to stick to the surface of your cell so they cannot escape and infect more of your cells.

The best way to protect your cell from the flu is to get the flu vaccine every year. You may receive the vaccine as a shot which contains dead versions of several types of the virus. Or you may receive it as a nasal spray which contains several types of live, but very weak forms of the virus. The vaccine exposes your body to several types of the influenza virus that are too weak to cause infection, but just strong enough to stimulate an immune response.

Within two weeks, cells in your immune system make markers called antibodies which are specific for only the type of flu you were exposed to. The antibodies attach to each flu virus and prevent it from attaching to your cells. Antibodies are also able to attach to more than one flu virus, which causes viruses to clump together. Your immune system responds to signals from the antibodies by engulfing and destroying the clumps of viruses. Later if you are exposed to these types of flu again, your body recognizes and destroys them, so you will not develop the flu from these same viruses. For continued protection against new flu viruses, you will need to get a flu vaccine every year.