International Biological Reference Preparations for Epidemic Infectious Diseases

Correlation between pseudotyped virus and authentic virus neutralisation assays, a systematic review and meta-analysis of the literature

Background

The virus neutralization assay is a principal method to assess the efficacy of antibodies in blocking viral entry. Due to biosafety handling requirements of viruses classified as hazard group 3 or 4, pseudotyped viruses can be used as a safer alternative. However, it is often queried how well the results derived from pseudotyped viruses correlate with authentic virus. This systematic review and meta-analysis was designed to comprehensively evaluate the correlation between the two assays.

Methods

Using PubMed and Google Scholar, reports that incorporated neutralisation assays with both pseudotyped virus, authentic virus, and the application of a mathematical formula to assess the relationship between the results, were selected for review. Our searches identified 67 reports, of which 22 underwent a three-level meta-analysis.

Results

The three-level meta-analysis revealed a high level of correlation between pseudotyped viruses and authentic viruses when used in an neutralisation assay. Reports that were not included in the meta-analysis also showed a high degree of correlation, with the exception of lentiviral-based pseudotyped Ebola viruses.

Conclusion

Pseudotyped viruses identified in this report can be used as a surrogate for authentic virus, though care must be taken in considering which pseudotype core to use when generating new uncharacterised pseudotyped viruses.

Overview of Neutralization Assays and International Standard for Detecting SARS-CoV-2 Neutralizing Antibody

We aimed to review the existing literature on the different types of neutralization assays and international standards for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We comprehensively summarized the serological assays for detecting neutralizing antibodies against SARS-CoV-2 and demonstrated the importance of an international standard for calibrating the measurement of neutralizing antibodies. Following the coronavirus disease outbreak in December 2019, there was an urgent demand to detect neutralizing antibodies in patients or vaccinated people to monitor disease outcomes and determine vaccine efficacy. Therefore, many approaches were developed to detect neutralizing antibodies against SARS-CoV-2, such as microneutralization assay, SARS-CoV-2 pseudotype virus assay, enzyme-linked immunosorbent assay (ELISA), and rapid lateral flow assay. Given the many types of serological assays for quantifying the neutralizing antibody titer, the comparison of different assay results is a challenge. In 2020, the World Health Organization proposed the first international standard as a common unit to define neutralizing antibody titer and antibody responses against SARS-CoV-2. These standards are useful for comparing the results of different assays and laboratories.

WHO International Standard for evaluation of the antibody response to COVID-19 vaccines: call for urgent action by the scientific community

The first WHO International Standard and International Reference Panel for anti-SARS-CoV-2 immunoglobulin were established by the WHO Expert Committee on Biological Standardization in December, 2020. The WHO International Antibody Standards are intended to serve as global reference reagents, against which national reference preparations or secondary standards can be calibrated. Calibration will facilitate comparison of results of assays (eg, of the neutralising antibody response to candidate COVID-19 vaccines) conducted in different countries. Use of these standards is expected to contribute to better understanding of the immune response, and particularly of the correlates of protection. This Personal View provides some technical details of the WHO Antibody Standards for SARS-CoV-2, focusing specifically on the use of these standards for the evaluation of the immune response to COVID-19 vaccines, rather than other applications (eg, diagnostic or therapeutic). The explanation with regard to why rapid adoption of the standards is crucial is also included, as well as how funders, journals, regulators, and ethics committees could drive adoption in the interest of public health.

Civil-Military Collaboration to Facilitate Rapid Deployment of a Mobile Laboratory in Early Response to COVID-19: A High-Readiness Exercise

Rapid and adaptable diagnostic capabilities are of great importance in the face of emerging infectious diseases. In an outbreak, timely establishment of diagnostic routines is crucial to identifying cases and preventing the spread of the disease, especially when faced with high-consequence pathogens. In this article, we describe a multiagency exercise including the rapid deployment and diagnostic adaptation of the Swedish Armed Forces mobile laboratory (biological field analysis laboratory) in the context of COVID-19. This deployment was initiated as a high-readiness exercise at the end of January 2020, when the global development of the outbreak was still uncertain. Through collaboration with the Public Health Agency of Sweden and a civilian hospital, a real-time reverse transcriptase polymerase chain reaction method specific to SARS-CoV-2 was made available and adapted to the mobile laboratory, and the team established and evaluated a functional and efficient diagnostic asset along with a logistical support chain. We also organized and evaluated mobile testing teams, and the method was later used in large-scale, national, cross-sectional COVID-19 surveys in several regions of Sweden. In this article, we focus on the challenges of overbridging the civil-military interface in this context and identifying lessons learned and added values to the response during the early pandemic. We propose that the experiences from this exercise and governmental agency collaboration are valuable in preparation for future outbreaks.

Severe Acute Respiratory Syndrome Coronavirus 2-Specific Antibody Responses in Coronavirus Disease Patients

A new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has recently emerged to cause a human pandemic. Although molecular diagnostic tests were rapidly developed, serologic assays are still lacking, yet urgently needed. Validated serologic assays are needed for contact tracing, identifying the viral reservoir, and epidemiologic studies. We developed serologic assays for detection of SARS-CoV-2 neutralizing, spike protein-specific, and nucleocapsid-specific antibodies. Using serum samples from patients with PCR-confirmed SARS-CoV-2 infections, other coronaviruses, or other respiratory pathogenic infections, we validated and tested various antigens in different in-house and commercial ELISAs. We demonstrated that most PCR-confirmed SARS-CoV-2-infected persons seroconverted by 2 weeks after disease onset. We found that commercial S1 IgG or IgA ELISAs were of lower specificity, and sensitivity varied between the 2 assays; the IgA ELISA showed higher sensitivity. Overall, the validated assays described can be instrumental for detection of SARS-CoV-2-specific antibodies for diagnostic, seroepidemiologic, and vaccine evaluation studies.

Severe Acute Respiratory Syndrome Coronavirus 2-Specific Antibody Responses in Coronavirus Disease Patients

A new coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has recently emerged to cause a human pandemic. Although molecular diagnostic tests were rapidly developed, serologic assays are still lacking, yet urgently needed. Validated serologic assays are needed for contact tracing, identifying the viral reservoir, and epidemiologic studies. We developed serologic assays for detection of SARS-CoV-2 neutralizing, spike protein–specific, and nucleocapsid-specific antibodies. Using serum samples from patients with PCR-confirmed SARS-CoV-2 infections, other coronaviruses, or other respiratory pathogenic infections, we validated and tested various antigens in different in-house and commercial ELISAs. We demonstrated that most PCR-confirmed SARS-CoV-2–infected persons seroconverted by 2 weeks after disease onset. We found that commercial S1 IgG or IgA ELISAs were of lower specificity, and sensitivity varied between the 2 assays; the IgA ELISA showed higher sensitivity. Overall, the validated assays described can be instrumental for detection of SARS-CoV-2–specific antibodies for diagnostic, seroepidemiologic, and vaccine evaluation studies.

Reliable Serological Diagnostic Tests for Arboviruses: Feasible or Utopia?

Infections with arthropod-borne viruses are increasing globally as a result of climate and demographic changes, global dispersion of insect vectors, and increased air travel. The similar symptomatology of arboviral diseases and the cocirculation of different arboviruses in Africa, Asia, and South America complicate diagnosis. Despite the high sensitivity and specificity of molecular diagnostic tests, their utility is limited to the short viremic phase of arbovirus infections, and therefore the diagnosis of infection is frequently missed in clinical practice. Conversely, the duration of antibody responses provides a wider window of opportunity, making diagnosis more dependent on IgM/IgG detection. This review discusses the issues underlying the low specificity of antibody-detection assays, and addresses the challenges and strategies for discovering more specific biomarkers to enable a more accurate diagnosis.

The Role of Reference Materials in the Research and Development of Diagnostic Tools and Treatments for Haemorrhagic Fever Viruses

Following the Ebola outbreak in Western Africa in 2013-16, a global effort has taken place for preparedness for future outbreaks. As part of this response, the development of vaccines, treatments and diagnostic tools has been accelerated, especially towards pathogens listed as likely to cause an epidemic and for which there are no current treatments. Several of the priority pathogens identified by the World Health Organisation are haemorrhagic fever viruses. This review provides information on the role of reference materials as an enabling tool for the development and evaluation of assays, and ultimately vaccines and treatments. The types of standards available are described, along with how they can be applied for assay harmonisation through calibration as a relative potency to a common arbitrary unitage system (WHO International Unit). This assures that assay metrology is accurate and robust. We describe reference materials that have been or are being developed for haemorrhagic fever viruses and consider the issues surrounding their production, particularly that of biosafety where the viruses require specialised containment facilities. Finally, we advocate the use of reference materials at early stages, including research and development, as this helps produce reliable assays and can smooth the path to regulatory approval.

Emerging infectious disease laboratory and diagnostic preparedness to accelerate vaccine development

Rapid vaccine development in response to an outbreak of a new emerging infectious disease (EID) is a goal targeted by public health agencies worldwide. This goal becomes more complicated when there are no standardized sets of viral and immunological assays, no accepted and well-characterized samples, standards or reagents, and no approved diagnostic tests for the EID pathogen. The diagnosis of infections is of critical importance to public health, but also in vaccine development in order to track incident infections during clinical trials, to differentiate natural infection responses from those that are vaccine-related and, if called for by study design, to exclude subjects with prior exposure from vaccine efficacy trials. Here we review emerging infectious disease biological standards development, vaccine clinical assay development and trial execution with the recent experiences of MERS-CoV and Zika virus as examples. There is great need to establish, in advance, the standardized reagents, sample panels, controls, and assays to support the rapid advancement of vaccine development efforts in response to EID outbreaks.