# Coronavirus Pandemic Explained How SARS\-CoV\-2 is built, how it jumps into people, and how it spreads through the air, cell by cell, during the COVID\-19 pandemic\. By cosmic\-badger\-e3b1a3e2 Topic: Human Body & Medicine [Open the interactive Jig](https://ask.jig.com/j/3xpzmpOr7E1C) ## Transcript ### 1. A tiny crown This is SARS\-CoV\-2, the virus that causes the illness COVID\-19\. A real one is only about 90 nanometres wide, so about 700 of them in a row would just span a human hair\. The spikes around it look like a crown, and corona is Latin for crown\. Real viruses have no colour\. Scientists add colours to pictures like this one so the parts are easy to tell apart\. ### 2. What is inside A thin, fatty skin called the envelope holds the virus together, studded with spike proteins\. Inside is its genome: one long strand of RNA, a recipe about 30,000 letters long, wrapped in beads of protein\. A virus cannot grow or copy itself on its own; it needs a living cell\. Because a virus is not a bacterium, antibiotics do not work against it\. ### 3. A jump from animals Late in 2019, people in the city of Wuhan, China, began catching a new illness\. Most evidence points to the virus jumping from animals sold at a market into people\. Bats carry very close relatives of it, and scientists are still studying the exact path it took\. A disease that jumps from animals to people is called a spillover\. ### 4. Carried on the air When an infected person breathes, talks, sings or coughs, they release droplets carrying the virus\. Big droplets fall to the ground within a metre or two\. Tiny ones, called aerosols, float and build up indoors, where someone nearby can breathe them in\. Opening windows and fresh air help clear aerosols away\. ### 5. A key in a lock Once breathed in, the virus meets cells lining the nose, throat and lungs\. Its spike fits a receptor called ACE2 on the cell surface, like a key in a lock\. Then the virus merges with the cell and slips its RNA recipe inside\. Sizes here are not to scale: a real cell is about a hundred times wider than the virus\. ### 6. A copy machine The cell reads the virus recipe as if it were its own and starts building new virus parts\. One infected cell can release thousands of fresh copies\. Each copy can go on to infect another cell, so the infection grows fast\. ### 7. Spreading before symptoms At first, each infected person passed the virus to about two or three others\. Many people spread it a day or two before they felt sick, and some never felt sick at all\. So it could travel quietly from person to person\. Each glowing figure is one infection\. Watch how quickly the glow branches outward\. ### 8. Around the world Because the virus was new, nobody had immunity, and planes carried it between cities within weeks\. On 11 March 2020 the World Health Organization called it a pandemic: a disease spreading across many countries and continents\. By then there were over 118,000 known cases in more than 110 countries\. Pandemic describes how widely a disease spreads, not how dangerous it is\. ### 9. Slowing it down Masks, distance, fresh air, testing and staying home when sick all cut the chains of spread\. From December 2020, vaccines taught bodies to recognise the spike before meeting the real virus\. Millions of people died, but science and care helped the world recover, and the global emergency ended in May 2023\. Turn protections on and off to see how breaking just a few links stops a chain\.