Seroprevalence

Seroprevalence is the proportion of individuals in a population who have detectable antibodies to a specific infectious agent or antigen at a given time. It is used to estimate past exposure and, when antibodies reflect vaccination, the level of vaccine-induced immunity at the population level. Seroprevalence studies typically test representative samples and project findings to the broader population.

Serological assays detect antibodies targeting particular antigens. Common methods include ELISA, chemiluminescent immunoassays, and virus neutralization tests. Results may reflect infection-induced or vaccine-induced antibodies, depending on the assay design and antigens used. Interpreting seroprevalence requires accounting for test sensitivity and specificity, as imperfect performance can bias estimates. Timing also matters: antibodies may rise after infection, possibly wane over time, and there is a window before seroconversion.

Seroprevalence is not a direct measure of immunity. The presence of antibodies does not guarantee protection, and protective thresholds may be unknown. Data can be affected by sampling biases, nonresponse, and cross-reactivity with related pathogens, as well as by differences in assay performance. Despite these limitations, seroprevalence studies provide useful information for public health: they help estimate cumulative exposure, calibrate burden models, guide vaccination strategies, and illuminate the true scale of outbreaks when reported case counts are incomplete.