Plaque- / Focus- Reduction Neutralization (PRNT / FRNT)

Plaque Reduction Neutralization Tests (PRNTs) and Focus Reduction Neutralization Tests (FRNTs) are highly robust cell-based assays that quantify functional virus-neutralizing antibody responses elicited by vaccination or natural infection. These assays are routinely used in VisMederi to evaluate immune responses against viruses such as SARS‑CoV‑2, influenza A and B, RSV, Oropouche, Monkeypox and Vaccinia, parainfluenza, Dengue, Zika, Yellow fever (Plaque reduction neutralization test (PRNT50) for the detection of anti-yellow fever antibodies from clinical samples), West Nile and Chikungunya.

PRNT / FRNT directly measure the ability of serum antibodies to inhibit virus replication and subsequent plaque / foci formation in susceptible cell monolayers. Heat‑inactivated serum samples are serially diluted and incubated with a standardized infectious dose of live virus prior to inoculation onto permissive cells. Following adsorption and overlay with a semi‑solid medium, plaques or foci formed by viral replication are detected by immunostaining using virus‑specific antibodies and an appropriate detection system. Neutralizing antibody titers are expressed as the reciprocal of the highest serum dilution resulting in a predefined percentage reduction (e.g. 50% or 90%) in the number of immunostained foci or plaque compared with virus control wells.

The PRNT / FRNT assays are applicable to a wide range of vaccine platforms, including mRNA, viral vector, inactivated, live‑attenuated, and recombinant technologies, and is frequently used as a confirmatory or reference neutralization method in vaccine immunogenicity studies.