Medicine & Health
What is Virus?
A virus is a tiny infectious agent that can only reproduce by hijacking the cells of a living host. Far smaller than bacteria, viruses sit on the edge of what counts as 'alive' — they're little more than genetic instructions wrapped in a protein shell.
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Watch a 2-minute lesson with voice + animation that explains virus.
Key things to understand
- 1A virus is genetic material (DNA or RNA) inside a protein coat, sometimes with an outer envelope.
- 2It can't grow or reproduce on its own — it must infect a host cell and use that cell's machinery to make copies.
- 3Viruses cause illnesses like the common cold, flu, COVID-19, and measles.
- 4Because they aren't fully alive and lack normal cell processes, antibiotics don't work on them — antivirals and vaccines do.
- 5Vaccines train the immune system to recognize a virus before you ever catch it.
Frequently asked questions
- Are viruses alive?
- It's debated. Viruses have genes and evolve, but they can't reproduce or carry out metabolism without a host cell, so many scientists place them between living and non-living.
- What's the difference between a virus and bacteria?
- Bacteria are living, single-celled organisms that reproduce on their own; viruses are much smaller, aren't truly alive, and need a host cell to multiply. Antibiotics kill bacteria, not viruses.
- Why don't antibiotics work on viruses?
- Antibiotics target processes in living bacterial cells. Viruses don't have those processes, so antibiotics can't affect them — antivirals and vaccines are used instead.