What are serologic assays for influenza surveillance?

From the previous post:

Some studies show that the virus is most readily isolated from specimens obtained from the lower respiratory tract,5,6 and since the course of clinical disease is not yet well defined, diagnosis may require repeated testing. It is also essential to determine the prevalence of MERS-CoV seropositivity in human and animal populations in Saudi Arabia and elsewhere in the Middle East to establish the likelihood of an epidemic and also to prevent one from occurring. This information is critical for an effective public health response. In addition to requiring vigilance by health care workers and public health authorities, obtaining these data is dependent on the generation of a validated serologic assay, which is not currently available.

Here is an excerpt on Serologic assays for influenza surveillance, diagnosis and vaccine evaluation:

Abstract

Serological techniques play a critical role in various aspects of influenza surveillance, vaccine development and evaluation, and sometimes in diagnosis, particularly for novel influenza virus infections of humans. Because individuals are repeatedly exposed to antigenically and genetically diverse influenza viruses over a lifetime, the gold standard for detection of a recent influenza virus infection or response to current vaccination is the demonstration of a seroconversion, a fourfold or greater rise in antibody titer relative to a baseline sample, to a circulating influenza strain or vaccine component. The hemagglutination-inhibition assay remains the most widely used assay to detect strain-specific serum antibodies to influenza. The hemagglutination-inhibition assay is also used to monitor antigenic changes among influenza viruses which are constantly evolving; such antigenic data is essential for consideration of changes in influenza vaccine composition. The use of the hemagglutinin-specific microneutralization assay has increased, in part, owing to its sensitivity for detection of human antibodies to novel influenza viruses of animal origin...continued
http://www.ncbi.nlm.nih.gov/pubmed/21692672