Vaccines and immune memory.

Step 1 of 6

A second meeting

After the virus is cleared, most of the plasma cells die, and the antibodies in the blood slowly fade. But some of the B and T cells that divided stay in the body as memory cells, sometimes for decades. They already fit the virus, and there are many more of them than at the first meeting.

A vaccine lets the body go through the first meeting without the illness. In the Scene you can choose in Vaccine a case in which the person was vaccinated before the virus landed. Days since infection stands at Three weeks on; after a vaccine, the chart shows the first meeting as a dashed grey line.

Step 2 of 6

Ten years on

The antibodies a vaccine makes do not stay in the blood for ever. Ten years after a vaccine very few are left. Vaccine is fixed at Ten years ago, and Days since infection at the day the virus lands.

Step 3 of 6

How high it gets

Even when you do not feel ill, the virus still gets in and multiplies a little before it is cleared. The upper chart shows how high it climbs, against the grey line of the first meeting.

Step 4 of 6

A stronger answer

The secondary response is not only faster. At every meeting the cells whose antibodies grip best divide most, so the antibodies improve. The lower chart shows the antibodies on a logarithmic scale.

Step 5 of 6

Staying well

Vaccine is yours. Switch between the three settings, and compare the virus on the upper chart with the dashed line of illness.

Step 6 of 6

What a vaccine does

Vaccines are built in several ways: a killed virus, a weakened one, one protein of the virus, or instructions our cells read to build that protein themselves. In the end they all do the same thing.