In nature, wild viruses adapted for transmission circulate in many animal species (bats, birds, primates…). Contamination of other animals, including humans, may occur by crossing of the species barrier. Genetic manipulations have been carried out on wild viruses to favor the species jumping and to increase of viral virulence. The aim was to identify the critical genes for pathogenicity. This has been mainly performed on potentially epidemic pathogens, as Myxovirus influenzae of avian flu and coronaviruses of SARS and MERS epidemics. These dangerous experiments were subject to a moratorium in the United States (2014-2017). Three years after the emergence of Covid-19, the origin of du SARS-CoV2 remains a mystery. Covid19 appeared in Wuhan, officially in December 2019, but probably during the autumn 2019. The virus was identified in January 2020. It belongs to the genus Betacoronavirus (subgenus Sarbecovirus). It was at once highly contagious. In addition, the primary isolates were genetically very homogeneous, differing only by two nucleotides without evidence for adaptive mutations. In addition, the Spike protein, a major virulence factor, has a furin site, not found in any other known sarbecovirus. Unlike the SARS and MERS epidemics, no intermediate host has been detected so far. Finally, no other outbreaks were reported at the beginning of the pandemic outside of Wuhan, contrary to what happened with the emergence of SARS (2002) and H7N9 avian influenza (2013). Today, there are two scenarios to explain the emergence of SARS-CoV2. Proponents of the natural origin argue that the bat virus might have directly infected humans, spreading silently at a low level in humans for years, without eliminating the existence of undetected intermediate hosts. This does not explain the origin in Wuhan, far away from the natural virus reservoirs. The furin site would have arisen spontaneously from other coronaviruses. The alternative scenario is that of a laboratory accident after gain-of-function manipulations from a SARS-like virus, or even the occurrence of a human contamination by a natural CoV virus grown on cells in Wuhan. This article is an update to the Quarterly Medical Review (QMR) devoted to the history of modern pandemics. To access this QMR contents, please go here: https://www.sciencedirect.com/journal/la-presse-medicale/vol/51/issue/3.
The COVID-19 pandemic affects the transplant recipients since March 2020. Transplant centers quickly organized themselves to optimize the management of the immunocompromised patients and to progress in the knowledge of this new disease. To this end, a French Registry was created, which includes all solid organ transplant patients who have developed a SARS Cov2 infection. Numerous studies have been carried out using these data to describe this new disease in transplant patients, to characterize its clinical and biological risk factors and to define its prognosis. The 60 days-mortality of transplant patients hospitalized for COVID-19 was evaluated at 23% and renal failure plays a major role in the poor prognosis in addition to the classical risk factors described in the general population. The advent of vaccination has been a great relief but transplanted patients have shown a poor vaccine response keeping them at risk of severe disease even after an adapted vaccination scheme. Specific strategies was proposed in this particularly fragile population like increasing vaccine doses or using anti SARS Cov-2 monoclonal antibodies.
The Covid-19 pandemic appeared in China in December 2019 as a cluster of transmissible pneumonia caused by a new betacoronavirus. On March 11, 2020, the World Health Organization (WHO) declared it a pandemic. Covid-19 is a mild infection in 80% of cases, serious in 15% and critical in 5%. Symptomatic forms include a first phase of flu-like viral invasion, and at times a second phase, dysimmune and inflammatory, with acute respiratory distress syndrome, multiorgan failure and thromboembolic complications. Degree of severity is related to age and comorbidities. SARS-CoV-2 is the third highly pathogenic Betacoronavirus to cross the species barrier. Its genome, an RNA of 29,903 nucleotides, shows strong homogeneity with bat coronaviruses from southern China, but the conditions for its passage in humans have yet to be elucidated. Mutations can give rise to variants of concern (VOC) that are more transmissible and able to evade the host's immune response. Several VOCs have succeeded and replaced one another: Alpha in October 2020, Beta and Gamma in December 2020, Delta in spring 2021 and Omicron in November 2021. The Covid-19 pandemic has evolved in five waves of unequal amplitude and severity, with geographical disparities. Worldwide, it has caused 395,000,000 confirmed cases including 5,700,000 deaths. Epidemiological surveillance applies several indicators (incidence rate, test positivity rate, effective R and occupancy rate of intensive care beds) supplemented by genomic monitoring to detect variants by sequencing. Non-pharmacological measures, particularly face mask wearing, have been effective in preventing the transmission of SARS-CoV-2. Few currently available drugs have proven useful, with the exception of dexamethazone for patients requiring oxygen therapy. Development of SARS-CoV-2 vaccines began early on many platforms. Innovation was brought about by the Pfizer-BioNTech and Moderna messenger RNA vaccines, which claim protective efficacy of 95% and 94.1% respectively, far higher than the 70% minimum set by the WHO. Governments have hesitated between two strategies, mitigation and suppression. The second has been favored in critical periods such as April 2020, when 2.5 billion people throughout the world were confined. Vaccination campaigns got underway at the end of December 2020 and progressed without reaching sufficient herd immunity, leading some nations to consider compulsory vaccination or to require a vaccine or health pass, in order for persons to access different activities. Will the pandemic stop with Omicron and become endemic? This part of the Covid-19 story remains to be told.
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