High-throughput identification of prefusion-stabilizing mutations in SARS-CoV-2 spike.

Designing prefusion-stabilized SARS-CoV-2 spike is critical for the effectiveness of COVID-19 vaccines. All COVID-19 vaccines in the US encode spike with K986P/V987P mutations to stabilize its prefusion conformation. However, contemporary methods on engineering prefusion-stabilized spike immunogens involve tedious experimental work and heavily rely on structural information. Here, we establish a systematic and unbiased method of identifying mutations that concomitantly improve expression and stabilize the prefusion conformation of the SARS-CoV-2 spike. Our method integrates a fluorescence-based fusion assay, mammalian cell display technology, and deep mutational scanning. As a proof-of-concept, we apply this method to a region in the S2 domain that includes the first heptad repeat and central helix. Our results reveal that besides K986P and V987P, several mutations simultaneously improve expression and significantly lower the fusogenicity of the spike. As prefusion stabilization is a common challenge for viral immunogen design, this work will help accelerate vaccine development against different viruses.

Probing the biophysical constraints of SARS-CoV-2 spike N-terminal domain using deep mutational scanning.

Increasing the expression level of the SARS-CoV-2 spike (S) protein has been critical for COVID-19 vaccine development. While previous efforts largely focused on engineering the receptor-binding domain (RBD) and the S2 subunit, the amino-terminal domain (NTD) has been long overlooked because of the limited understanding of its biophysical constraints. In this study, the effects of thousands of NTD single mutations on S protein expression were quantified by deep mutational scanning. Our results revealed that in terms of S protein expression, the mutational tolerability of NTD residues was inversely correlated with their proximity to the RBD and S2. We also identified NTD mutations at the interdomain interface that increased S protein expression without altering its antigenicity. Overall, this study not only advances the understanding of the biophysical constraints of the NTD but also provides invaluable insights into S-based immunogen design.

Immunity certification for COVID-19: ethical considerations.

Restrictive measures imposed because of the coronavirus disease 2019 (COVID-19) pandemic have resulted in severe social, economic and health effects. Some countries have considered the use of immunity certification as a strategy to relax these measures for people who have recovered from the infection by issuing these individuals a document, commonly called an immunity passport. This document certifies them as having protective immunity against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the virus that causes COVID-19. The World Health Organization has advised against the implementation of immunity certification at present because of uncertainty about whether long-term immunity truly exists for those who have recovered from COVID-19 and concerns over the reliability of the proposed serological test method for determining immunity. Immunity certification can only be considered if scientific thresholds for assuring immunity are met, whether based on antibodies or other criteria. However, even if immunity certification became well supported by science, it has many ethical issues in terms of different restrictions on individual liberties and its implementation process. We examine the main considerations for the ethical acceptability of immunity certification to exempt individuals from restrictive measures during the COVID-19 pandemic. As well as needing to meet robust scientific criteria, the ethical acceptability of immunity certification depends on its uses and policy objectives and the measures in place to reduce potential harms, and prevent disproportionate burdens on non-certified individuals and violation of individual liberties and rights.

Les restrictions imposées dans le cadre de la lutte contre la pandémie de maladie à coronavirus 2019 (COVID-19) ont eu de lourdes conséquences économiques, sociales et sanitaires. Certains pays ont envisagé la mise en place d'une stratégie visant à alléger ces restrictions pour les individus guéris en leur octroyant un document communément appelé «passeport d'immunité¼. Ce document atteste qu'ils ont développé une immunité protectrice contre le coronavirus 2 du syndrome respiratoire aigu sévère (SARS-CoV-2), le virus à l'origine de la COVID-19. L'Organisation mondiale de la Santé a déconseillé l'usage du certificat d'immunité pour l'instant, car l'incertitude demeure quant à l'existence réelle d'une immunité à long terme pour ceux qui se sont remis de la COVID-19. En outre, la fiabilité des tests sérologiques censés déterminer si l'individu est immunisé n'est pas avérée. Un tel certificat ne peut être instauré que si les seuils scientifiques en matière d'immunité sont respectés, qu'ils soient fondés sur les anticorps ou sur d'autres critères. Néanmoins, même si le certificat d'immunité est désormais bien accepté par la science, il s'accompagne de nombreuses questions d'ordre éthique en ce qui concerne la limitation des libertés individuelles et la mise en œuvre. Dans le présent document, nous examinons les principales considérations à prendre en compte pour garantir l'acceptabilité éthique du certificat d'immunité visant à lever les mesures de restriction pour certaines personnes durant la pandémie de COVID-19. Cette acceptabilité éthique dépend non seulement de son degré de conformité à des critères scientifiques stricts, mais aussi de son usage, des objectifs politiques ainsi que des mesures mises en place pour atténuer les préjudices potentiels et éviter d'imposer une charge disproportionnée sur les individus dépourvus de certificat, ou de bafouer les droits et libertés de tout un chacun.

Las medidas restrictivas impuestas a causa de la pandemia de la enfermedad coronavirus de 2019 (COVID-19) han tenido graves efectos sociales, económicos y sanitarios. Algunos países han considerado la posibilidad de utilizar la certificación de inmunidad como estrategia para flexibilizar dichas medidas para las personas que se han recuperado de la infección mediante la expedición a dichas personas de un documento, comúnmente denominado pasaporte de inmunidad. Este documento certifica que han desarrollado inmunidad protectora contra el coronavirus-2 del síndrome respiratorio agudo severo (SARS-CoV-2), el virus que causa la COVID-19. La Organización Mundial de la Salud ha desaconsejado la aplicación de la certificación de la inmunidad en la actualidad debido a la incertidumbre sobre si existe realmente una inmunidad a largo plazo para quienes se han recuperado de la COVID-19 y a las preocupaciones sobre la fiabilidad del método de prueba serológica propuesto para determinar la inmunidad. La certificación de la inmunidad solo puede considerarse si se cumplen los umbrales científicos para asegurar la inmunidad, ya sea que se basen en anticuerpos o en otros criterios. Sin embargo, incluso si la certificación de la inmunidad llegara a estar bien respaldada por la ciencia, tiene muchas cuestiones éticas en cuanto a las diferentes restricciones de las libertades individuales y su proceso de aplicación. Examinamos las principales consideraciones sobre la aceptabilidad ética de la certificación de la inmunidad para eximir a los individuos de las medidas restrictivas durante la pandemia de la COVID-19. Además de necesitar cumplir criterios científicos sólidos, la aceptabilidad ética de la certificación de inmunidad depende de sus usos y objetivos de política y de las medidas que se apliquen para reducir los posibles daños y evitar que se impongan cargas desproporcionadas a las personas que no cuenten con dicha certificación y se violen las libertades y derechos individuales.

Top five ethical lessons of COVID-19 that the world must learn.

As the world reflects upon one year since the first cases of coronavirus disease 2019 (COVID-19) and prepare for and experience surges in cases, it is important to identify the most crucial ethical issues that might lie ahead so that countries are able to plan accordingly. Some ethical issues are rather obvious to predict, such as the ethical issues surrounding the use of immunity certificates, contact tracing, and the fair allocation of vaccines globally. Yet, the most significant ethical challenge that the world must address in the next year and beyond is to ensure that we learn the ethical lessons of the first year of this pandemic. Learning from our collective experiences thus far constitutes our greatest moral obligation. Appreciating that decision-making in the context of a pandemic is constrained by unprecedented complexity and uncertainty, beginning in June 2020, an international group of 17 experts in bioethics spanning 15 countries (including low-, middle-, and high-income countries) met virtually to identify what we considered to be the most significant ethical challenges and accompanying lessons faced thus far in the COVID-19 pandemic. Once collected, the group met over the course of several virtual meetings to identify challenges and lessons that are analytically distinct in order to identify common ethical themes under which different challenges and lessons could be grouped. The result, described in this paper, is what this expert group consider to be the top five ethical lessons from the initial experience with COVID-19 that must be learned.

A Strategy to Prevent and Control Zoonoses?

The authors argue that in preventing and controlling the pandemic of Covid-19, we should have taken an offensive or proactive strategy rather than a defensive or reactionary one because the former type of approach can bring about more health benefits and fewer harms than can the latter. The offensive or proactive approach consists of two parts: The first part is to preemptively establish a barrier between a novel virus and humans in order to prevent the spillover of the virus into humans, and the second part is that, when a spillover fails to be prevented, we should take public interventions, such as contact tracing, social distancing, and quarantine and isolation, as early as when there are several dozens or one hundred or more cases that manifest symptoms with an unknown etiology in order to prevent an epidemic that is still limited to relatively small groups from developing into an outbreak.