Theory 16/Life, Medicine & Mind /Vaccinology
Durability Is a Cell Ratio
Durability is read from antibody titres. The ratio behind them may decide the slope.
Vaccine durability is set by the ratio of long-lived plasma cells to memory B cells at a threshold, so a vaccine that generates many memory cells but few plasma cells will lose protection quickly despite strong initial titres.
01The evidence
Antibody decay rates vary widely between vaccines with similar peak titres, which suggests the cellular composition differs.
02The tension
Models predict durability from peak titre, which assumes a common decay constant and fails to predict the differences.
03The mechanism
Titre is maintained by plasma cells and replenished by memory cells on re-exposure. A high plasma-cell fraction maintains titre without re-exposure; a high memory fraction produces a sharp peak and a rapid fall.
That makes the ratio the determinant, and predicts decay rate should be predictable from the composition at peak.
04What this is not
Peak models extrapolate from the maximum. This predicts the slope from composition.
05Predictions
- P1Decay should track the plasma-to-memory ratio.
- P2Equal peak titres should decay differently.
- P3Composition should predict durability better than titre.
06Refutation
Decay tracking peak titre alone would restore the titre model.
07What it changes
It would change how vaccine candidates are compared.