How a vaccine trains your immune system, in 3D

What the simulation shows

• Viruses (spiky balls) drifting in towards a cell covered in receptors.
• One virus's spike locking onto a receptor on the cell, like a key in a lock (a flash).
• The virus slipping inside the cell and releasing its genes (a glowing strand).
• The hijacked cell building copies of the virus, one after another; the count climbs about tenfold a day.
• The new viruses bursting out of the cell to infect others.
• Y-shaped antibodies swarming in and sticking to the viruses, blocking their spikes; the virus count falls.
• A killer T cell docking onto the infected cell and destroying it.
• Memory cells remain, a callout: remembered for years, the next attack stopped in hours.
• A vaccine: harmless spike pieces with no virus inside; antibodies form and are already waiting.

The real numbers it runs on

The simulation is built on these facts, so the narration and the picture always agree:

• A virus is genes in a protein shell; it can't copy itself, so it must get inside a living cell.
• Its spike proteins fit receptors on the cell's surface like a key in a lock; that's how it gets in.
• Inside, the virus's genes make the cell build new viruses; one cell can release thousands of copies, and the count in the body can grow about tenfold a day.
• Antibodies are Y-shaped proteins that stick to the virus's spikes so it can't enter cells, and mark it for destruction; making the right ones takes about a week the first time.
• Killer T cells find infected cells and destroy them, stopping the factory.
• Memory cells remain for years, so a second infection is stopped within hours or days, often before you feel sick.
• A vaccine shows the immune system a harmless piece of the virus (like its spike), so the antibodies and memory are ready before the real virus arrives.
• The fever and aches of being ill are mostly the immune system fighting, not the virus itself.
• Your body has about 30 trillion cells.

The script this video was made from

“How a vaccine trains you”: the narration of the video above. Each highlighted moment in the simulation happens on the word that names it.

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