Seroprevalence

Seroprevalence is the proportion of people in a defined population whose blood serum contains detectable antibodies against a particular infectious agent. It indicates population-level evidence of previous exposure, whether through natural infection or, depending on the antibody and test used, vaccination. It does not directly measure the number of people currently infected.

What it reveals

A representative serosurvey can reveal infections that routine case counts miss, including asymptomatic or unreported infections.

• Overall seroprevalence estimates how widely an infectious agent has circulated in the tested population.
• Age-specific seroprevalence helps identify patterns of cumulative exposure across age groups.
• Repeated surveys can show changes in exposure over time and support vaccination and disease-control planning.

How it is measured

Blood samples from a defined population are tested for pathogen-specific antibodies, and the number testing positive is divided by the total number tested. Reliable estimates require representative sampling and appropriate laboratory assays.

• Test sensitivity and specificity can affect the estimated proportion.
• Results may vary according to the antibody measured, the timing of sampling and antibody waning.
• Vaccination and cross-reactive antibodies may complicate interpretation.

Limits and dengue relevance

Seropositivity is evidence of an immune response, not proof of active infection, complete immunity or absence of future disease.

• For dengue, antibodies may cross-react because the virus has four serotypes.
• A positive result can indicate prior dengue exposure but does not by itself establish durable protection against every serotype.
• Population seroprevalence can inform vaccine policy, but individual vaccination decisions require validated tests and applicable public-health guidance.

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