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Will SARS-CoV-2 become endemic?


Reinfection, in which an individual is subject to multiple, distinct infections from the same virus species throughout their lifetime, is a salient feature of many respiratory viruses. Indeed, the persistence and ubiquity in human society of common respiratory viruses—including influenza viruses, respiratory syncytial virus (RSV), rhinovirus, and the endemic coronaviruses—are largely due to their ability to produce repeat infection. Since the emergence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for the ongoing coronavirus disease 2019 (COVID-19) pandemic, a critical concern has been whether humans will experience reinfections with this pathogen, which might enable it to become endemic. Typically, following an initial infection, the human adaptive immune system develops a suite of defenses, including memory B lymphocytes capable of producing neutralizing antibodies targeted to bind to that particular pathogen, and memory T lymphocytes that help regulate immune responses and induce death of infected cells. These adaptive immune components, particularly B cells, can produce sterilizing immunity in which the pathogen, if reintroduced to the host, is prevented from replicating within the body. However, for many viruses, a number of processes, particularly insufficient adaptive immune response, waning immunity, and immune escape, can undermine or circumvent the sterilizing character of immunity and allow subsequent reinfection. In the first instance, an initial infection with a particular agent may not engender an adaptive immune response sufficient to confer sterilizing immunity. Serological studies indicate that most SARS-CoV-2 infections, regardless of severity, induce development of some specific antibodies ([ 1 ][1]); however, despite encouraging results from the experimental vaccination of primates, it remains unclear whether those antibodies are sufficient to provide long-term effective protection or if other adaptive immune components are present and functional. Furthermore, immune response to SARS-CoV-2 infection is heterogeneous, with individuals who experience asymptomatic infections manifesting a weaker immune response than those experiencing more severe disease ([ 1 ][1]). It is possible that some individuals never develop sterilizing immunity following infection with SARS-CoV-2, or that multiple exposures will be needed for affinity maturation and development of long-lasting protection. ![Figure][2] Factors influencing postpandemic transmission of SARS-CoV-2 Rates of repeat infection, factors modulating seasonality, competition with other circulating respiratory viruses, and control measures will influence the endemic pattern of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. GRAPHIC: C. BICKEL/ SCIENCE Waning immunity, in which the initial adaptive immune response is robust and protective but dissipates over time, leaving the host vulnerable to reinfection, may also undermine sterilizing immunity. Immune escape is a third process that can facilitate reinfection, in particular by viruses. Here, a virus, during its continued serial passage through a host population, accumulates point mutations. This accumulation, termed antigenic drift, may lead to conformational changes of viral surface proteins that disrupt the binding of antibodies previously generated against an earlier variant. Immune escape is a consequence of this antigenic drift that enables reinfection through the evasion of adaptive protection. The time scales of waning immunity and immune escape differ by pathogen and have yet to be defined for SARS-CoV-2. Thus far, the mutation rate of the SARS-CoV-2 genome appears to be slower than that of influenza viruses. This lower rate may be a consequence of proof-reading during replication, which is exclusive to coronaviruses among RNA viruses. Conversely, human coronavirus (HCoV) OC43 is highly variable, particularly in genes encoding surface proteins such as the spike protein, indicating that considerable diversification can occur. To date, some evidence of SARS-CoV-2-specific antibody waning has been captured in a longitudinal study ([ 2 ][3]), and a few verified repeat SARS-CoV-2 infections have been documented ([ 3 ][4]). Although reinfections can occur, the number of reinfection cases is not currently sufficient to generalize the duration of immunity at population scales or the severity of repeat infection. Whether reinfections will be commonplace, how often they will occur, how contagious reinfected individuals will be, and whether the risk of severe clinical outcomes changes with subsequent infection remain to be understood. Insight from other respiratory viruses points to the possibility of reinfection with SARS-CoV-2. Naturally acquired infections with the four endemic HCoVs (OC43, HKU1, 229E, and NL63) indicate that reinfections with the same HCoV type are common within 1 year ([ 4 ][5]); sequential infections with the same influenza virus strain can occur in less than 2 years ([ 5 ][6]); and reinfections of adults with RSV within 1 year have also been documented ([ 6 ][7]). By contrast, more pathogenic viruses that induce systemic effects on the host may elicit a longer-lasting adaptive immune response. For example, longitudinal immune profiles from SARS survivors showed a stronger immune response with neutralizing antibodies persisting for 2 to 5 years ([ 7 ][8]). However, it could not be confirmed if and for how long this response conferred immunity because the SARS outbreak lasted less than 1 year. In addition to duration of protective immunity, the long-term effects of SARS-CoV-2 on humans will depend on the severity of reinfection. Sequential infections with influenza virus have been associated with less severe symptoms ([ 8 ][9]), whereas no association between reinfection and symptom severity was found in recurring endemic HCoV infections ([ 4 ][5]). In addition, for other viruses (e.g., RSV and dengue), suboptimal binding of naturally induced or vaccine-induced antibodies can enhance infection severity upon subsequent exposure, a phenomenon called antibody-dependent enhancement (ADE) ([ 9 ][10]). To date, responses among the few patients with verified SARS-CoV-2 reinfection have been heterogeneous with one apparent repeat infection requiring hospitalization. Thus, thorough serological and prospective studies are needed to determine whether ADE manifests among SARS-CoV-2 infections, either because of prior homologous infection or cross-reactive antibodies from other HCoVs. This will have particular relevance for vaccines and convalescent plasma therapy. Should reinfection prove commonplace, and barring a highly effective vaccine delivered to most of the world's population, SARS-CoV-2 will likely become endemic ([ 10 ][11]). The typical time scale at which individuals experience reinfection and seasonal differences in transmissibility will determine the pattern of endemicity. Outside the tropics, the incidence of many common respiratory virus infections increases during particular times of the year. This phase-locked behavior is due to accumulated susceptibility to reinfection, which increases over time because of immune escape and waning immunity, and seasonal modulation of virus transmissibility derived from environmental conditions, changing behavior (e.g., mixing indoors in cold weather), or altered immune function. For example, influenza incidence is greatest during winter in temperate regions. Once expelled from an infectious host, the influenza virus appears to be more stable in low-humidity conditions ([ 11 ][12]), which are prevalent both indoors and outdoors during winter. Further, during colder months, people spend more time indoors and school is in session, which may facilitate transmission, and shorter days and less sunlight exposure may suppress immune function. The endemic HCoVs (OC43, HKU1, NL63, and 229E) all exhibit a seasonality in temperate regions, similar to influenza viruses ([ 12 ][13]). Consequently, numerous studies have sought to determine whether conditions such as temperature, sunlight, humidity, ozone, and pollution affect SARS-CoV-2 viability and transmissibility. The results are not currently conclusive, although it appears that environmental conditions, such as sunlight and humidity, may modulate SARS-CoV-2 transmissibility—not enough to preclude transmission during the first waves of the pandemic when immunity is generally low—but perhaps sufficient to favor seasonal, phase-locked transmission during winter in temperate regions, similar to influenza virus, once immunity increases. Like the 2009 influenza pandemic, the continued circulation by SARS-CoV-2 following this initial pandemic period will manifest as a function of reinfection rates, vaccine availability and efficacy, and social, immune, and innate factors that modulate virus transmissibility (see the figure). In addition, the cyclic persistence of SARS-CoV-2 in human populations may be affected by ongoing opportunities for interaction with other respiratory pathogens. Co-circulating respiratory viruses may interfere with one another while competing for the same resources, and their interactions have been studied at population and individual levels, in reconstructed human tissues and in animal models. The outcomes in individuals experiencing serial exposure to different viruses vary and in general appear to depend on the order and timing of exposures. Many studies have documented evidence of negative interference between viruses caused by short-lived (days) protection elicited from the first infection. Host antiviral interferon responses are often regarded as the main mechanism by which interference manifests; that is, as a result of a recent infection, the host cells up-regulate the synthesis of interferons, potentially inhibiting a secondary infection. Even though it is short-lived, this effect can be strong at population scales and temporarily reduce the prevalence of a virus or shift the timing of its circulation. For example, it is hypothesized that a large summer 2009 rhinovirus outbreak delayed pandemic influenza virus emergence in Europe ([ 13 ][14]). The clinical and population-scale interactions of SARS-CoV-2 with other respiratory viruses, particularly influenza viruses and other HCoVs, need to be monitored in the coming years. To date, some SARS-CoV-2 coinfections have been documented ([ 14 ][15]), including coinfections with influenza and RSV; however, testing for multiple pathogens has not been routinely carried out, and the scarce data that do exist, mostly for older adults with high rates of preexisting medical conditions, do not support a definitive evaluation of coinfection likelihood or severity. Studies prior to the pandemic indicate that simultaneous infections with multiple respiratory viruses are not uncommon but are not associated with increased disease severity. At the population scale, a possible overlap between influenza and SARS-CoV-2 outbreaks poses a serious threat to public health systems. Seasonal influenza produces millions of severe infections worldwide every year, and this additional burden could be catastrophic on systems already challenged by the COVID-19 pandemic. Conversely, given similar modes of transmission among different respiratory viruses, the nonpharmaceutical interventions adopted to mitigate SARS-CoV-2 transmission (personal protective equipment, social distancing, increased hygiene, limited indoor gatherings) may reduce the magnitude of seasonal influenza outbreaks. Such increased use of nonpharmaceutical measures, and possible virus interference, could be responsible for the reduced incidence of influenza during the recent winter of the Southern Hemisphere ([ 15 ][16]). The phases and magnitudes of different outbreaks in a multipathogen system are dictated by the interaction dynamics between those pathogens: from large overlapping phases when pathogens enhance one another's transmission, to complete inhibition of a strain by the neutralizing cross-reactivity of a more transmissible one ([ 9 ][10]). Several postpandemic scenarios for SARS-CoV-2 have been modeled ([ 10 ][11]), postulated on duration of immunity and cross-immunity between SARS-CoV-2 and the other betacoronaviruses (OC43 and HKU1). A duration of immunity similar to that of the other betacoronaviruses (∼40 weeks) could lead to yearly outbreaks of SARS-CoV-2, whereas a longer immunity profile, coupled with a small degree of protective cross-immunity from other betacoronaviruses, could lead to the apparent elimination of the virus followed by resurgence after a few years. Other scenarios are, of course, possible, because there are many processes at play and much that remains unresolved. 1. 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Coronavirus And Mental Illnesses: Is COVID-19 Linked To Psychosis?

International Business Times

Ever since the COVID-19 pandemic began, most of the research on the virus has focused on its direct effects on the human body with the aim of finding a possible cure or an effective treatment. However, the researchers at John Hopkins University are investigating a potential secondary long-term impact of COVID-19 exposure- higher susceptibility to psychosis. "Over the years there have been data showing an association between exposure to general respiratory viruses such as the flu and subsequent psychotic episodes. This association was especially evident in studies of the aftermath of the great influenza of 1918," Emily Severance, Ph.D., assistant professor of pediatrics, Johns Hopkins University, Baltimore, Maryland, told Medscape Medical News. The research team is also analyzing if the association with psychosis was specific to influenza or if other respiratory infections including the coronavirus might also have similar consequences.

What the Coronavirus Does Inside the Body: Anatomy of a Killer

Der Spiegel International

The best way to learn more about SARS-CoV-2 is to start small. Coronaviruses are a mere 160 nanometers in size. In order to multiply, the tiny pathogens are reliant on the cells belonging to a different organism. The novel coronavirus likely comes from bat viruses, and it is thought that, even before it made the jump to humans, it developed the mechanism allowing it to bind with human cells. Some bat viruses are able to bind to a receptor called ACE2.

Sorting out viruses with machine learning – ScienceDaily


The ongoing global pandemic has created an urgent need for rapid tests that can diagnose the presence of the SARS-CoV-2 virus, the pathogen that causes COVID-19, and distinguish it from other respiratory viruses. Now, researchers from Japan have demonstrated a new system for single-virion identification of common respiratory pathogens using a machine learning algorithm trained on changes in current across silicon nanopores. This work may lead to fast and accurate screening tests for diseases like COVID-19 and influenza.In a study published this month in ACS Sensors scientists at Osaka University have introduced a new system using silicon nanopores sensitive enough to detect even a single virus particle when coupled with a machine learning algorithm.In this method, a silicon nitride layer just 50 nm thick suspended on a silicon wafer has tiny nanopores added, which are themselves only 300 nm in diameter. When a voltage difference is applied to the solution on either side of the wafer, ions travel through the nanopores in a process called electrophoresis.The motion of the ions can be monitored by the current they generate, and when a viral particle enters a nanopore, it blocks some of the ions from passing through, leading to a transient …

China Coronavirus Expert Warns COVID-19 Is 'Just The Tip Of The Iceberg'

International Business Times

Dr. Shi Zhengli, the Chinese virologist from Wuhan whose intensive work on bat coronaviruses quickly allowed scientists to come to grips with COVID-19, is sounding the alarm anew this new disease is only one of many set to strike the world. She also called for scientists worldwide to unite in this new fight and assailed politics for complicating the scientific response to emerging pandemic diseases. Called "Bat Woman" for her work with bat coronaviruses, Dr. Shi said the new viruses now being discovered worldwide are "just the tip of the iceberg." "If we want to prevent human beings from suffering from the next infectious disease outbreak, we must go in advance to learn of these unknown viruses carried by wild animals in nature and give early warnings," Dr. Shi told Chinese state-run television network, CGTN. ""If we don't study them there will possibly be another outbreak." Dr. Shi is adamant bat-borne coronaviruses will cause more disease outbreaks in the future. SARS (severe acute respiratory syndrome) is another bat-borne virus. "These viruses exist in nature whether we admit it or not," she said. "If we don't study them, there will possibly be another outbreak, and we wouldn't know them.