An update on lateral flow immunoassay for the rapid detection of SARS-CoV-2 antibodies

Abstract

Over the last three years, after the outbreak of the COVID-19 pandemic, an unprecedented number of novel diagnostic tests have been developed. Assays to evaluate the immune response to SARS-CoV-2 have been widely considered as part of the control strategy. The lateral flow immunoassay (LFIA), to detect both IgM and IgG against SARS-CoV-2, has been widely studied as a point-of-care (POC) test. Compared to laboratory tests, LFIAs are faster, cheaper and user-friendly, thus available also in areas with low economic resources. Soon after the onset of the pandemic, numerous kits for rapid antibody detection were put on the market with an emergency use authorization. However, since then, scientists have tried to better define the accuracy of these tests and their usefulness in different contexts. In fact, while during the first phase of the pandemic LFIAs for antibody detection were auxiliary to molecular tests for the diagnosis of COVID-19, successively these tests became a tool of seroprevalence surveillance to address infection control policies. When in 2021 a massive vaccination campaign was implemented worldwide, the interest in LFIA reemerged due to the need to establish the extent and the longevity of immunization in the vaccinated population and to establish priorities to guide health policies in low-income countries with limited access to vaccines. Here, we summarize the accuracy, the advantages and limits of LFIAs as POC tests for antibody detection, highlighting the efforts that have been made to improve this technology over the last few years.

Keywords: COVID-19; IgG; IgM; SARS-CoV-2; lateral flow immunoassay; neutralizing antibodies; point of care test; rapid antibody test.

Figure 1.. Schematic view of a LFIA for the detection of SARS-CoV-2 IgG/IgM. If antibodies are present in the sample a complex is formed with the SARS-CoV-2 antigen tagged nanoparticles and the anti-human IgG immobilized on the nitrocellulose membrane. A signal will be observed in the test line where the anti-IgG is captured, a signal must be visible also on the control line indicating the correct execution of the test (from Ernst et al. ref n.40).

Figure 2.. Timing for effective anti-SARS-CoV-2 IgA, IgM and IgG detection and the 343 relationship with the detection of SARS-CoV-2 RNA in different samples (from Falzone L et al. ref n. 144).