Definitions of terms used in this article

CorrelateAn immune response that is responsible for and statistically interrelated with protection
Absolute correlateA specific level of response highly correlated with protection; a threshold
Relative correlateA level of response variably correlated with protection
CocorrelateOne of two or more factors that correlate with protection in alternative, additive, or synergistic ways
SurrogateAn immune response that substitutes for the true immunologic correlate of protection, which may be unknown or not easily measurable