The word virus is Latin for “slimy liquid” or “poison.”

Viruses are the smallest of microbes. They can cause flu, polio, yellow fever, smallpox, and other diseases, like COVID-19.

 To survive, viruses have to take over other living cells. This is what makes them so deadly—you must kill the cell they have invaded in order to kill the virus.

A virus is a strand of genetic material covered with a protein shell. The genetic material inside a virus lets it copy itself once it has invaded a cell. A virus may also be covered by proteins called antigens that help it invade healthy cells.

Our immune system recognizes a virus by its antigens. When a virus reproduces, if often changes (including its antigens.) And so, the virus may go undetected in your body. A big change in the antigens of a virus may lead to an epidemic. Why? Because so few people would have any immunity to the new virus. This is what happened during the 2020 COVID-19 pandemic.

Influenza (flu) virus is good at changing easily and quickly. This is why scientists have to come up with a new flu vaccine each year. They hope to match the vaccine with the new strain of flu. And that’s why instead of having long-term immunity to the flu, we need to get a new vaccine each year.

Getting a disease and surviving it can produce antibodies and immunity, but not always. You may or may not have antibodies. They may go away. Immunity is not always a given. That is another reason vaccines are so important. 

While we take antibiotics for many illnesses, they do not work against viruses. Some viral diseases do have vaccines. Scientists are working on antivirals (which are not as powerful as antibiotics) in hopes of preventing diseases. After COVID-19 began to infect people, scientists around the world raced to develop an effective vaccine for this deadly disease.