What it shows
The first time your body meets a germ, the primary immune response is slow and small: it takes about a week before antibodies appear, and the level stays fairly low. But the body keeps memory cells. The next time the same germ (or a vaccine made from it) turns up, the secondary response starts within a couple of days, climbs many times higher and lasts much longer. Vaccines and boosters work by giving the body that first meeting safely.
This page draws the antibody level against time for up to three events (a vaccine dose or the real germ), a dashed protective level, and a table of each response’s lag, peak and memory. A second card shows one antibody molecule: tap its parts to learn what each does.
It fits Class 12 Biology: human health and disease (immunity: innate and acquired, active and passive, vaccination and immunisation, the structure of an antibody). The cells involved are drawn in cell explorer; what happens across a whole town is in epidemic model, and why vaccinating most people protects everyone is in herd immunity.
This is a teaching model. The numbers are round and made up, in arbitrary units. Real responses differ between people and germs. Not medical advice.
How to use it
- Pick a story, or set your own: each of the three events can be Nothing, a Vaccine dose or a Germ (infection), on any day from 0 to 330.
- Slide the protective level: above it, the model says the germ is stopped before it can make the person ill.
- Slide the memory boost: how many times bigger the IgG peak of the first secondary response is than in the primary one.
- Switch Total antibodies to IgM and IgG to see the two classes separately, and tick Log scale to see small levels too.
- Read the sentence under the graph, the facts (days protected, rounds of memory, second peak ÷ first) and the table.
Worked example
In Infection, then the same germ again, the germ arrives on day 10 and again on day 100, with protective level 2 and memory boost × 10. The first response starts 6 days later and peaks at 1.3 on day 21: below the protective line. The second starts after only 2 days and peaks at about 6.47 on day 107, five times higher, and it falls much more slowly. The second peak ÷ first is × 5, and the level is at or above 2 on 67 days of the year.
Options explained
- Vaccine dose: in this model a dose triggers 60 % of the response a germ would, because a vaccine does not multiply.
- Germ: if the level is already above the protective line on the day it arrives, the page says the person is protected.
- IgM and IgG: IgM (dashed) is the first antibody made and fades fast. IgG takes over and dominates the secondary response.
Check yourself
Five questions: three on ideas (which response is faster, active and passive immunity, antibody chains, which cells make antibodies) and two with numbers (halving after the peak, and the day a second response starts). Nothing is saved.
FAQ
Why do some vaccines need boosters? One dose gives a primary response and some memory cells. A booster gives a secondary response: a far higher, longer-lasting level and more memory.
Are these real antibody numbers? No. They are teaching values chosen to show the shape. Real levels are measured in labs in many different units.
Is this from my textbook? It covers the standard school topic with its own model and examples. It is an independent study aid, not part of any board or publisher.
Where the numbers come from
- Standard school immunology: primary and secondary (anamnestic) responses, IgM before IgG, memory B cells, active and passive immunity, vaccination and boosters, and the H₂L₂ antibody structure. Written for fibub; no textbook text, figures or exercises are used.
- The curves are a teaching model with round, made-up numbers in arbitrary units (lags of 6 and 2 days, half-lives of 5, 20 and 40 days, a 10-fold memory boost you can change). They show the pattern, not real measurements, and are not medical advice.
- Checked against a separate Python version of the same model (plain loops and numpy) for the levels, peaks and protected days of two stories.
Standard scientific values, such as constants, atomic weights and melting points, are facts found in every textbook; we name where ours were checked. If you are an author or publisher and want a value, a credit or a table changed or removed, tell us and we will act quickly.
Last updated 2026-11-09.