Abstract
Since their first documentation in 1952, plaque reduction neutralization tests (PRNTs) have become the choice of test for the measurement of neutralizing antibodies against a particular virus. However, PRNTs can be performed only against viruses that cause cytopathic effects (CPE). PRNTs also require skilled personnel and can be time-consuming depending on the time required for the virus to cause CPE. Hence, their application limits large-scale studies or epidemiological and laboratory investigations. Since 1978, many surrogate PRNTs or immunocolorimetric assay (ICA)-based focus reduction neutralization tests (FRNT) have been developed. In this article, ICAs and their utility in FRNTs for the characterization of neutralizing antibodies, homologous or heterologous cross-neutralization, and laboratory diagnosis of viruses of public health importance have been discussed. Additionally, possible advancements and automations have been described that may help in the development and validation of novel surrogate tests for emerging viruses.