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What is a virus?
Medicine & HealthLesson on requestFree to read
Quick answer
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.
Key things to understand
- A virus is genetic material (DNA or RNA) inside a protein coat, sometimes with an outer envelope.
- It can't grow or reproduce on its own — it must infect a host cell and use that cell's machinery to make copies.
- Viruses cause illnesses like the common cold, flu, COVID-19, and measles.
- Because they aren't fully alive and lack normal cell processes, antibiotics don't work on them — antivirals and vaccines do.
- Vaccines train the immune system to recognize a virus before you ever catch it.
People also ask
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.
How do viruses make you sick?
They invade cells and force them to produce more viruses, damaging tissue and triggering immune responses.