Bradford Hill's 'Biological gradient (dose–response relationship)' as a measure of causation (one of several with temporality, biological plausibility etc.) STRONGLY seen in graph by Shrestha et al.

Shrestha et al. examined effectiveness of COVID Bivalent booster & graph shows clear dose response & fits Bradford Hill's 'Biological gradient in pointing to causality; greater exposure=greater effect

SOURCE:

https://www.medrxiv.org/content/10.1101/2022.12.17.22283625v1.full.pdf

Biological gradient (dose–response relationship): Greater exposure should generally lead to greater incidence of the effect.