#asymptomatiques

Assessment of Day-7 Postexposure Testing of Asymptomatic Contacts of #COVID-19 Patients to Evaluate Early Release from Quarantine — Vermont, May–November 2020 | MMWR
▻https://www.cdc.gov/mmwr/volumes/70/wr/mm7001a3.htm

Seulement 3% des sujets contact ont eu un #PCR #sars-cov2 positif à J7,

1,26% des sujets #contact #asymptomatiques étaient positifs à J7

Aucun des négatifs à J7 ne s’est déclaré positif dans les 7 jours suivant.

977 (44.9%) of these contacts had a specimen collected for testing on day 7. Among these, 34 (3%) had test results that were positive, 940 (96%) had results that were negative, and three (<1%) had results that were indeterminate (Table). Among the 34 contacts who received a positive SARS-CoV-2 PCR test result on day 7 after exposure, 12 (35%) were asymptomatic. The remaining 22 contacts with positive test results were symptomatic at the time of testing; approximately one half had developed symptoms on days 4–7 after exposure. Among the 940 contacts who received negative test results on specimens collected on day 7 after exposure, 154 (16%) had a subsequent test within the next 7 days (i.e., days 8–14); among these, 152 (99%) had tests that remained negative, and two (1%) had results that were indeterminate.

#COVID-19 : premiers résultats d’une étude d’envergure menée grâce aux collaborateurs de l’Institut Curie sur la réponse immunitaire contre le SARS-CoV-2
▻https://www.pasteur.fr/fr/espace-presse/documents-presse/covid-19-premiers-resultats-etude-envergure-menee-grace-aux-collaborateurs-i

Près de 1 850 collaborateurs volontaires de l’Institut Curie, représentatifs d’une population active francilienne, ont participé à Curie-O-SA, une étude sérologique lancée en mai dernier en collaboration avec l’Institut Pasteur. Avec un taux d’infection au virus SRAS-CoV-2 compris entre 11 et 16,6% (dont 21% de personnes asymptomatiques), ces résultats révèlent donc une forte prévalence de l’immunisation et des réponses immunitaires plutôt brèves. Dans 5% des cas, l’infection est prouvée par un test RT-PCR mais ne conduit pas à la production d’anticorps. A la Une du numéro de janvier 2021 de l’European Journal of Immunology, cette étude est prolongée pendant un an.

[...]

Par ailleurs, dans les sérums obtenus 4 à 8 semaines après le premier prélèvement, les analyses ont mis en évidence que la durée de demi-vie (c’est-à-dire le temps pour que la concentration d’anticorps diminue de 50%) des anticorps neutralisants n’était que de 4 semaines. Au cours d’études rétrospectives, ceci pourrait entraîner une sous-estimation de la prévalence réelle de l’infection. Néanmoins, la perte des anticorps spécifiques circulants ne signifie pas nécessairement la perte de protection. En effet la séroconversion s’accompagne d’une persistance des cellules T et B « mémoires » spécifiques prolongeant l’immunité des individus.

#asymptomatiques #immunité

Towards an accurate and systematic characterisation of persistently asymptomatic infection with #SARS-CoV-2 - The Lancet Infectious Diseases
▻https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(20)30837-9/abstract

Two systematic reviews that only included studies with sufficient time to exclude pre-symptomatic infection have estimated the proportion of SARS-CoV-2 infections that remain completely free of symptoms to be 20% (95% CI 17–25%)7 and 17% (95% CI 14–20%).8 The individual studies included in these reviews rarely estimated an asymptomatic fraction greater than 50%. The range of estimates of asymptomatic SARS-CoV-2 infection reported in studies that used a wider variety of study designs goes from as low as 4% to more than 80% (table).9

#asymptomatiques

Post-lockdown #SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China
▻https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7679396

No new symptomatic cases and 300 asymptomatic cases (detection rate 0.303/10,000, 95% CI 0.270–0.339/10,000) were identified. There were no positive tests amongst 1,174 close contacts of asymptomatic cases.

Une étude chinoise permet-elle de conclure que les asymptomatiques « ne contaminent personne » ? | LCI
▻https://www.lci.fr/sante/covid-19-une-etude-chinoise-permet-elle-de-conclure-que-les-asymptomatiques-ne-c

En conclusion, rien ne permet donc aujourd’hui de conclure que les patients asymptomatiques « ne contaminent personne ». L’étude chinoise citée par des internautes est intéressante aux yeux des spécialistes, mais ne peut être avancé comme une preuve viable. Divers travaux publiés lors des derniers jours ont par ailleurs mis en évidence des cas de transmission du #Covid-19 par des personnes #asymptomatiques, laissant clairement entendre que l’épidémie se propageait de manière régulière sans aucune manifestation visible.

#contagiosité

#Transmission of #SARS-COV-2 Infections in Households — Tennessee and Wisconsin, April–September 2020 | MMWR
►https://www.cdc.gov/mmwr/volumes/69/wr/mm6944e1.htm

https://www.cdc.gov/mmwr/volumes/69/wr/social-media/mm6944e1_TransmissionInHouseholdsCOVID19_IMAGE_30Oct20_1200x627.jpg

Étude prospective (et en cours) sur la transmission du virus dans les foyers familiaux,

– proportion de contacts contaminés : étonnamment élevée

Among these 191 contacts, 102 had SARS-CoV-2 detected in either nasal or saliva specimens during follow-up, for a secondary infection rate of 53% (95% confidence interval [CI] = 46%–60%).

– #contagiosité en fonction de l’âge : les #enfants ne sont pas en reste et pas seulement les adolescents,

Among fourteen households in which the index patient was aged <18 years, the secondary infection rate from index patients aged <12 years was 53% (95% CI = 31%–74%) and from index patients aged 12–17 years was 38% (95% CI = 23%–56%).

– délai de positivité du PCR chez les personnes contaminées : court

Approximately 75% of secondary infections were identified within 5 days of the index patient’s illness onset, and substantial transmission occurred whether the index patient was an adult or a child.

– proportion de personnes #asymptomatiques au moment de la positivité du PCR (60%) et combien le restent (33%- sur un suivi de 7 jours) :

Forty percent (41 of 102) of infected household members reported symptoms at the time SARS-CoV-2 was first detected by RT-PCR. During 7 days of follow-up, 67% (68 of 102) of infected household members reported symptoms, which began a median of 4 days (IQR = 3–5) after the index patient’s illness onset.

Proportion de personnes PCR positifs asymptomatiques pour l’ensemble des contacts : 18%

The rates of symptomatic and asymptomatic laboratory-confirmed SARS-CoV-2 infection among household members was 36% (95% CI = 29%–43%) and 18% (95% CI = 13%–24%), respectively.

Enseignements :

These findings suggest that transmission of SARS-CoV-2 within households is high, occurs quickly, and can originate from both children and adults.

An important finding of this study is that fewer than one half of household members with confirmed SARS-CoV-2 infections reported symptoms at the time infection was first detected, and many reported no symptoms throughout 7 days of follow-up, underscoring the potential for transmission from asymptomatic secondary contacts and the importance of quarantine. Persons aware of recent close contact with an infected person, such as a household member, should quarantine in their homes and get tested for SARS-CoV-2

Occurrence and #transmission potential of asymptomatic and presymptomatic #SARS-CoV-2 infections: A living systematic review and meta-analysis
▻https://journals.plos.org/plosmedicine/article?id=10.1371/journal.pmed.1003346

Background

There is disagreement about the level of asymptomatic severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. We conducted a living systematic review and meta-analysis to address three questions: (1) Amongst people who become infected with SARS-CoV-2, what proportion does not experience symptoms at all during their infection? (2) Amongst people with SARS-CoV-2 infection who are asymptomatic when diagnosed, what proportion will develop symptoms later? (3) What proportion of SARS-CoV-2 transmission is accounted for by people who are either asymptomatic throughout infection or presymptomatic?

Methods and findings
[..,] We included a total of 94 studies. The overall estimate of the proportion of people who become infected with SARS-CoV-2 and remain asymptomatic throughout infection was 20 % (95% confidence interval [CI] 17–25) with a prediction interval of 3%–67% in 79 studies that addressed this review question. There was some evidence that biases in the selection of participants influence the estimate. In seven studies of defined populations screened for SARS-CoV-2 and then followed, 31% (95% CI 26%–37%, prediction interval 24%–38%) remained asymptomatic. The proportion of people that is presymptomatic could not be summarised, owing to heterogeneity. The secondary attack rate was lower in contacts of people with asymptomatic infection than those with symptomatic infection (relative risk 0.35, 95% CI 0.10–1.27). Modelling studies fit to data found a higher proportion of all SARS-CoV-2 infections resulting from transmission from presymptomatic individuals than from asymptomatic individuals . Limitations of the review include that most included studies were not designed to estimate the proportion of asymptomatic SARS-CoV-2 infections and were at risk of selection biases; we did not consider the possible impact of false negative RT-PCR results, which would underestimate the proportion of asymptomatic infections; and the database does not include all sources.

Conclusions

The findings of this living systematic review suggest that most people who become infected with SARS-CoV-2 will not remain asymptomatic throughout the course of the infection. The contribution of presymptomatic and asymptomatic infections to overall SARS-CoV-2 transmission means that combination prevention measures, with enhanced hand hygiene, masks, testing tracing, and isolation strategies and social distancing, will continue to be needed.

#asymptomatiques #pré-symptomatiques

Three Quarters of People with #SARS-CoV-2 Infection are Asymptomatic : A | CLEP
▻https://www.dovepress.com/three-quarters-of-people-with-sars-cov-2-infection-are-asymptomatic-an-pe

Plus précisément, 75% de ceux qui se révèlent positifs lors d’un dépistage de masse sont #asymptomatiques au moment du prélèvement.

#Covid : more than 80% of positive UK cases in study had no core symptoms | World news | The Guardian
▻https://www.theguardian.com/world/2020/oct/08/more-than-80-positive-cases-in-covid-study-had-no-core-symptoms

Three quarters who tested positive had no notable symptoms at all, the scientists found when they checked whether people reported other ailments such as fatigue and breathlessness on the day of testing.

Unlike #coronavirus testing in the community which focuses on people with symptoms, the ONS infection survey routinely tests tens of thousands of households around the country whether the occupants have symptoms or not.

Maître Pandaï sur Twitter : « Le taux de positivité chez les asymptomatiques testés est au-dessus de 4%, ce qui est élevé (il serait de 0,x% sur un échantillon représentatif de la population). Ces #asymptomatiques testés sont donc bien surexposés. ▻https://t.co/qjEUeq2pYc » / Twitter
▻https://twitter.com/Panda31808732/status/1311777633840041986

Saliva** or Nasopharyngeal Swab Specimens for Detection of #SARS-CoV-2 | NEJM
▻https://www.nejm.org/doi/full/10.1056/NEJMc2016359

https://www.nejm.org/na101/home/literatum/publisher/mms/journals/content/nejm/2020/nejm_2020.383.issue-13/nejmc2016359/20200918/images/img_small/nejmc2016359_f1.jpeg

Rapporté en français ci-dessous :

Test de détection salivaire du SARS-Co V2 - Revue Médicale Suisse
▻https://www.revmed.ch/covid-19/Test-de-detection-salivaire-du-SARS-Co-V2

Un total de 70 patients hospitalisés atteints de #Covid-19 ont fourni le cadre de l’étude. Après confirmation de l’infection par un échantillon sur écouvillon nasopharyngé, des échantillons supplémentaires nasopharyngés et salivaires des patients ont été prélevés.

L’analyse a démontré la présence de plus de copies d’ARN du SRAS-CoV-2 dans les échantillons de salive que dans l’échantillon sur écouvillon nasopharyngés.

En outre, un pourcentage plus élevé d’échantillons de salive sont restés positifs au court du temps en comparaison avec les échantillons sur écouvillon nasopharyngé. Ces résultats suggèrent que les échantillons de salive ont au moins une sensibilité similaire que les échantillons sur écouvillon nasopharyngien dans la détection du SRAS-CoV-2 au cours de l’hospitalisation. L’analyse des variations de la concentration d’ARN au cours de l’évolution clinique a mis en évidence des fluctuations moins importantes dans la salive que dans les prélévements nasopharyngés.

Dans trois cas, un échantillon d’écouvillon nasopharyngé négatif a été suivi d’un écouvillon positif lors de la prochaine collecte d’un échantillon. Ce phénomène ne s’est produit qu’une seule fois avec les échantillons de salive.

L’étude s’est aussi intéressée à des personnes #asymptomatiques. 495 agents de santé asymptomatiques ont fourni du matériel pour tester à la fois des échantillons de salive et de nasopharynx. Sur 13 agents de santé positifs lors de l’examen salivaire, 9 avaient collecté des échantillons sur écouvillon nasopharyngien appariés le même jour, et 7 de ces échantillons se sont révélés négatifs Le diagnostic des 13 agents de santé a été confirmé par la suite par des tests diagnostiques d’échantillons nasopharyngés supplémentaires.

Commentaire

Les moyens de diagnostic évoluent et il est important de souligner un apport prometteur d’un prélèvement salivaire plus aisé à pratiquer et mieux accepté des patients que les frottis nasopharyngés actuels.

L’article du NEJM ajoute aussi que le choix de ce test permet aux services de santé de ne pas être débordés/exposés et est une réponse aux pénuries d’équipement de protection et de matériel de prélèvement,

Collection of saliva samples by patients themselves negates the need for direct interaction between health care workers and patients. This interaction is a source of major testing bottlenecks and presents a risk of nosocomial infection. Collection of saliva samples by patients themselves also alleviates demands for supplies of swabs and personal protective equipment. Given the growing need for testing, our findings provide support for the potential of saliva specimens in the diagnosis of SARS-CoV-2 infection.

Méthode d’auto-recueil de l’échantillon de salive :
▻https://www.nejm.org/doi/suppl/10.1056/NEJMc2016359/suppl_file/nejmc2016359_appendix_1.pdf

Saliva samples were self-collected by the patient using the methods described. Upon waking, patients were asked to avoid food, water and brushing of teeth until the sample was collected. Patients were asked to repeatedly spit into a sterile urine cup until roughly a third full of liquid (excluding bubbles), before securely closing it. All samples were stored at room temperature and transported to the research lab at the Yale School of Public Health within 5 hours of sample collection and tested within 12 hours of sample collection. While a stabilizing solution was not added to the saliva, recent work has demonstrated that SARS-CoV-2 RNA is stable in saliva stored at room temperature for up to 25 days.

#tests #salive #diagnostics

Transmission Dynamics of COVID-19 Outbreaks Associated with Child Care Facilities — Salt Lake City, Utah, April–July 2020 | MMWR
▻https://www.cdc.gov/mmwr/volumes/69/wr/mm6937e3.htm

https://www.cdc.gov/mmwr/volumes/69/wr/social-media/mm6937e3_COVID19OutbreaksChildCare_IMAGE_11Sept20_1200x675-medium.jpg

What is already known about this topic?

Children aged ≥10 years have been shown to transmit SARS-CoV-2 in school settings.

What is added by this report?

Twelve children acquired COVID-19 in child care facilities. Transmission was documented from these children to at least 12 (26%) of 46 nonfacility contacts (confirmed or probable cases). One parent was hospitalized. Transmission was observed from two of three children with confirmed, asymptomatic COVID-19.

What are the implications for public health practice?

SARS-CoV-2 Infections among young children acquired in child care settings were transmitted to their household members. Testing of contacts of laboratory-confirmed COVID-19 cases in child care settings, including children who might not have symptoms, could improve control of transmission from child care attendees to family members.

Your #Coronavirus Test Is Positive. Maybe It Shouldn’t Be. - The New York Times
►https://www.nytimes.com/2020/08/29/health/coronavirus-testing.html

https://static01.nyt.com/images/2020/08/30/science/30virus-test-print/22VIRUS-TEST-facebookJumbo.jpg

Au lieu d’éliminer les #asymptomatiques de la sélection des sujets testés, les experts interrogés sont en faveur de l’utilisation de tests de détection d’#antigènes viraux, qui sont moins sensibles que les tests PCR (mais pouvant être très spécifiques ▻https://www.cdc.gov/coronavirus/2019-ncov/lab/resources/antigen-tests-guidelines.html), en partant du principe qu’en-dessous d’une certaine #charge_virale on aurait peu de chances d’être contagieux.

Some of the nation’s leading public health experts are raising a new concern in the endless debate over coronavirus testing in the United States: The standard tests are diagnosing huge numbers of people who may be carrying relatively insignificant amounts of the virus.

Most of these people are not likely to be contagious, and identifying them may contribute to bottlenecks that prevent those who are contagious from being found in time. But researchers say the solution is not to test less, or to skip testing people without symptoms, as recently suggested by the Centers for Disease Control and Prevention.

Instead, new data underscore the need for more widespread use of rapid tests, even if they are less sensitive.

“The decision not to test asymptomatic people is just really backward,” said Dr. Michael Mina, an epidemiologist at the Harvard T.H. Chan School of Public Health, referring to the C.D.C. recommendation.

“In fact, we should be ramping up testing of all different people,” he said, “but we have to do it through whole different mechanisms.”

#covid-19 #contagiosité #sars-cov2 #transmission

#Prevalence of SARS-CoV-2 Infection in Children Without Symptoms of #Coronavirus Disease 2019 | Infectious Diseases | JAMA Pediatrics | JAMA Network
▻https://jamanetwork.com/journals/jamapediatrics/fullarticle/2769878

Overall, 250 of 33 041 children (age range, 0-18 years) without symptoms who were tested at 28 hospitals were positive for SARS-CoV-2 through May 29, 2020. Across the 25 CSAs represented by these children’s hospitals, prevalence varied from 0% to 2.2%, with a pooled prevalence of 0.65% (95% CI, 0.47%-0.83%, with significant heterogeneity; Figure 1). Asymptomatic pediatric prevalence was significantly associated with weekly incidence of COVID-19 in the general population during the 6-week period over which most testing of individuals without symptoms occurred (unstandardized coefficient B = 1.07 [95% CI, 0.60-1.54]; P < .001; Figure 2A). No other factor (CSA population, number of tests performed, region, testing indication, or sample collection site) demonstrated a significant association with prevalence in individuals without symptoms.

#enfants #sars-cov2 #asymptomatiques

Early Release - Clinical Course of Asymptomatic and Mildly Symptomatic Patients with Coronavirus Disease Admitted to Community Treatment Centers, South Korea - Volume 26, Number 10—October 2020 - Emerging Infectious Diseases journal - CDC
▻https://wwwnc.cdc.gov/eid/article/26/10/20-1620_article

Les critères ne sont pas seulement cliniques mais dépendent aussi de l’âge et des facteurs de risque :

We used KCDC guidelines to classify patients. Asymptomatic patients were defined as persons <50 years of age with no underlying conditions who were nonsmokers and had a body temperature of <37.5°C without taking antipyretic drugs. Mildly symptomatic patients were defined as persons <50 years of age with >1 underlying condition and a temperature of <38°C with antipyretic drugs.

Les personnes ainsi concernées sont placés dans des centres d’#isolement médicalisés.

Abstract

We evaluated the clinical course of asymptomatic and mildly symptomatic patients with laboratory-confirmed coronavirus disease (#COVID-19) admitted to community treatment centers (CTCs) for isolation in South Korea.

Of 632 patients, 75 (11.9%) had symptoms at admission, 186 (29.4%) were asymptomatic at admission but developed symptoms during their stay, and 371 (58.7%) remained asymptomatic during their entire clinical course.

Nineteen (3.0%) patients were transferred to hospitals , but 94.3% (573/613) of the remaining patients were discharged from CTCs upon virologic remission.

The mean virologic remission period was 20.1 days (SD + 7.7 days). Nearly 20% of patients remained in the CTCs for 4 weeks after diagnosis.

The virologic remission period was longer in symptomatic patients than in asymptomatic patients. In mildly symptomatic patients, the mean duration from symptom onset to virologic remission was 11.7 days (SD + 8.2 days). These data could help in planning for isolation centers and formulating self-isolation guidelines.

#asymptomatiques

Early Release - Antibody Responses to #SARS-CoV-2 at 8 Weeks Postinfection in Asymptomatic Patients - Volume 26, Number 10—October 2020 - Emerging Infectious Diseases journal - CDC
▻https://wwwnc.cdc.gov/eid/article/26/10/20-2211_article

We compared levels of severe acute respiratory syndrome coronavirus 2 neutralizing antibodies in recovery plasma from 7 completely asymptomatic coronavirus disease patients with those in symptomatic patients in South Korea. We found that serologic diagnostic testing was positive for 71% (5/7) of completely asymptomatic patients, but neutralizing antibody response occurred in all 7 patients.

Neutralizing antibodies play an essential role in virus clearance and have been considered a critical immune player for protection against viral diseases. Knowledge of the neutralizing antibody response in asymptomatic patients is critical for diagnosing the disease, understanding pathogenesis, and interpreting seroepidemiologic data to define prevalence and risk factors for infection. Production of neutralizing antibodies in asymptomatic COVID-19 patients was reported recently. Wu et al. reported that ≈30% of recovered mild COVID-19 patients generated a deficient level of neutralizing antibody titers; in 10 of the 175 patients, the level was below the limit of detection (F. Wu et al., unpub. data, ▻https://doi.org/10.1101/2020.03.30.20047365External Link). The difference in results from our study compared with the previous study might be caused by differences in the timing of the test. In the previous study, antibody tests were performed 2–3 weeks after symptom onset, whereas we tested 2 months after symptom onset or laboratory diagnosis. #Seroconversion in asymptomatic patients might take longer .

#asymptomatique #asymptomatiques #anticorps #sérologie #immunité

COVID-19 : #Asymptomatique, une personne en contamine 71 autres en prenant un ascenseur - Marie Claire
▻https://www.marieclaire.fr/covid-19-asymptomatique-elle-contamine-71-personnes-en-prenant-un-ascens

https://cache.marieclaire.fr/data/photo/w600_h315_ci/5r/ascenseur-news-corona.jpg

C’est après avoir séjourné aux États-Unis qu’une habitante de la province de Heilongjiang en Chine, qui avait pourtant respecté les mesures de quatorzaine imposées et avait été testée négative au COVID-19, a contaminé 71 personnes.

Asymptomatique, elle aurait transmis le virus en empruntant l’ascenseur de sa résidence, donc sans avoir de contact direct avec quiconque. Les chercheurs chinois alertent de la situation dans une publication de la revue américaine Emerging Infectious Diseases.

#coronavirus

Part des formes asymptomatiques et transmission du #SARS-CoV-2 en phase pré-symptomatique. Synthèse rapide #COVID-19.
▻https://www.santepubliquefrance.fr/import/part-des-formes-asymptomatiques-et-transmission-du-sars-cov-2-en

Nous [...] établissons une distinction entre les personnes infectées ne développant jamais de symptômes après un suivi suffisant pour exclure leur survenue (forme #asymptomatique au sens strict), et les personnes sans symptômes au moment de leur confirmation biologique (incluant les formes #asymptomatiques et #pré-symptomatiques). Nous nous intéressons à la proportion de formes asymptomatiques et au potentiel de #transmission en phase #pré-symptomatique ou d’#incubation. Il en ressort que près d’un quart des infections par le SARS-CoV-2 restent asymptomatiques et que dans un contexte de recherche active des contacts, environ 50% des transmissions surviennent durant la phase pré-symptomatique du patient source. Nous n’avons pas trouvé d’élément pour caractériser le potentiel de transmission des formes complètement silencieuses de l’infection .

Dernière mise à jour de l’#OMS sur les modes de #transmission du #SARS-CoV-2 et les implications pour la #prévention et les #précautions ;
▻https://www.who.int/publications-detail-redirect/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution
▻https://apps.who.int/iris/rest/bitstreams/1286634/retrieve

L’OMS, tout en acceptant l’hypothèse de la transmission par #aérosol, continue de donner une importance plus grande aux gouttelettes et elle persiste à estimer que les cas #asymptomatiques sont peu contagieux.

La partie sur la transmission est résumée par Helen Branswell sur Twitter : ▻https://mobile.twitter.com/helenbranswell/status/1281274685616001024

WHO issued an update on how #Covid19 transmits. It says:

a) In some cases/places short-term aerosol transmission can’t be ruled out, though droplet & fomite transmission could also explain these cases.

b) Most transmission occurs via droplets, from symptomatic people." /

c) most transmission seems to occur when people have symptoms or just before they develop symptoms.

d) it’s not clear how often people who are truly asymptomatic — never have symptoms — transmit. Percentage thought to be low

e) Fomites (virus on surfaces) are considered a likely mode of transmission, but no clear cases yet.

f) Not clear if transmission through blood is possible; risk seems low.

Robust T cell immunity in convalescent individuals with asymptomatic or mild #COVID-19 | bioRxiv
▻https://www.biorxiv.org/content/10.1101/2020.06.29.174888v1

SARS-CoV-2-specific memory T cells will likely prove critical for long-term immune protection against COVID-19. We systematically mapped the functional and phenotypic landscape of SARS-CoV-2-specific T cell responses in a large cohort of unexposed individuals as well as exposed family members and individuals with acute or convalescent COVID-19. Acute phase SARS-CoV-2-specific T cells displayed a highly activated cytotoxic phenotype that correlated with various clinical markers of disease severity, whereas convalescent phase SARS-CoV-2-specific T cells were polyfunctional and displayed a stem-like memory phenotype. Importantly, SARS-CoV-2-specific T cells were detectable in antibody-seronegative family members and individuals with a history of asymptomatic or mild COVID-19 . Our collective dataset shows that #SARS-CoV-2 elicits robust memory T cell responses akin to those observed in the context of successful vaccines, suggesting that natural exposure or infection may prevent recurrent episodes of severe COVID-19 also in seronegative individuals.

Immunity to COVID-19 is probably higher than tests have shown
▻https://medicalxpress.com/news/2020-06-immunity-covid-higher-shown.html

https://scx2.b-cdn.net/gfx/news/hires/2020/20-covid19.jpg

“T cells are a type of white blood cells that are specialized in recognizing virus-infected cells, and are an essential part of the immune system,” says Marcus Buggert, assistant professor at the Center for Infectious Medicine, Karolinska Institutet, and one of the paper’s main authors. “Advanced analyses have now enabled us to map in detail the T-cell response during and after a COVID-19 infection. Our results indicate that roughly twice as many people have developed T-cell immunity compared with those who we can detect antibodies in .”

Coronavirus: Immunity may be more widespread than tests suggest - BBC News
▻https://www.bbc.com/news/health-53248660

https://ichef.bbci.co.uk/news/1024/branded_news/16E01/production/_113179639_f0302380-t_cell_targeting_covid-19_viruses_illustration.jpg

T-cells are very complex and much harder to identify than antibodies, requiring specialist labs and small batches of samples being tested by hand over the course of days.

This means mass testing for T-cells is not a very likely prospect at the moment.

#immunité #séronégatifs #asymptomatiques

Coronavirus à #Ischgl : 40% des habitants de la station de ski [sont porteurs d’anticorps].
▻https://www.altitude.news/business/2020/07/04/coronavirus-ischgl-nombreux-habitants-malades-immunite

https://i0.wp.com/www.altitude.news/wp-content/uploads/2020/07/ischgl-vue.jpg?fit=865%2C605&ssl=1

En début d’année, la station autrichienne d’Ischgl avait fait la une de l’actualité. En pleine crise du #coronavirus, elle avait été un cluster important, contaminant plusieurs visiteurs qui, rentrés chez eux, avaient répandu la maladie. [..,]

Les chercheurs de l’Université de médecine d’Innsbruck viennent de réaliser des tests sérologiques sur quelques 1.473 habitants de la station. Le résultat montre que 42,4% d’entre eux sont porteurs d’#anticorps. Preuve tangible d’une forme d’exposition massive de ces habitants à la maladie. La plupart n’ont pourtant pas été considérés comme malades du #covid-19 (en anglais). 85% de ses porteurs d’anticorps ont donc au la surprise d’apprendre qu’ils avaient été malades sans le savoir.

#asymptomatiques #immunité #sars-cov2 #sérologie #séroprévalence

Almost half in virus-hit Austria ski resort have antibodies: study
▻https://medicalxpress.com/news/2020-06-virus-hit-austria-resort-antibodies.html

Among those under 18 years old, just 27 percent had antibodies, which could be because they had less contact to infected people or because their immune system reacts differently to the virus, according to epidemiologist Peter Willeit.

Article d’origine:
Ischgl-Studie: 42,4 Prozent sind Antikörper-positiv
▻https://www.i-med.ac.at/pr/presse/2020/40.html

Clinical and immunological assessment of asymptomatic .#SARS-CoV-2 infections | Nature Medicine
►https://www.nature.com/articles/s41591-020-0965-6

https://media.springernature.com/m685/springer-static/image/art%3A10.1038%2Fs41591-020-0965-6/MediaObjects/41591_2020_965_Fig1_HTML.png

You May Have Antibodies After #Coronavirus Infection. But Not for Long. - The New York Times
▻https://www.nytimes.com/2020/06/18/health/coronavirus-antibodies.html

https://static01.nyt.com/images/2020/06/18/science/18VIRUS-ANTIBODIES/18VIRUS-ANTIBODIES-facebookJumbo.jpg

It’s a question that has haunted scientists since the pandemic began: Does everyone infected with the virus produce antibodies — and if so, how long do they last?

Not very long, suggests a new study published Thursday in Nature Medicine. Antibodies — protective proteins made in response to an infection — may last only two to three months, especially in people who never showed symptoms while they were infected.

The conclusion does not necessarily mean that these people can be infected a second time, several experts cautioned. Even low levels of powerful neutralizing antibodies may still be protective, as are the immune system’s T cells and B cells.

But the results offer a strong note of caution against the idea of “immunity certificates” for people who have recovered from the illness, the authors suggested.

Coronavirus : pour les malades sans symptômes, l’#immunité [humorale] face au #Covid-19 pourrait être plus faible - Sud Ouest.fr
▻https://www.sudouest.fr/2020/06/18/coronavirus-pour-les-malades-sans-symptomes-l-immunite-face-au-covid-19-pou

Huit semaines après la sortie de l’hôpital, les niveaux d’#anticorps neutralisants, qui confèrent a priori une immunité contre le virus, avaient diminué chez 81,1% des patients sans symptômes, contre 62,2% chez les patients symptomatiques.

#asymptomatiques

Hospital-Wide #SARS-CoV-2 Antibody Screening in 3056 Staff in a Tertiary Center in Belgium | Health Care Workforce | JAMA | JAMA Network
▻https://jamanetwork.com/journals/jama/fullarticle/2767382

IgM non recherché car test non fiable

Internal validation of the assay using 90 polymerase chain reaction–confirmed cases and 101 historic biobanked samples found a sensitivity of 92.2% and specificity of 97.0% for IgG.

Dr Zoë Hyde sur Twitter :
“Study of 3,056 hospital staff in Belgium, of which 6.4% had #SARSCoV2 antibodies. Of the 197 staff with antibodies, 15% were asymptomatic. Prior loss of smell strongly associated with having antibodies, more than fever or cough. #COVID” / Twitter
▻https://twitter.com/DrZoeHyde/status/1272840521610702853

https://pbs.twimg.com/media/EaoJs-RVcAEJ_-Q?format=jpg&name=900x900#.jpg

#Belgique #séroprévalence #asymptomatiques #immunité #anticorps #soignants

Natural history and transmission potential of asymptomatic #SARS-CoV-2 infection | Clinical Infectious Diseases | Oxford Academic
▻https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciaa711/5851471

Background
Little is known about the natural history of asymptomatic SARS-CoV-2 infection or its contribution to infection transmission.

Methods
We conducted a prospective study at a quarantine center for COVID-19 in Ho Chi Minh City, Vietnam. We enrolled quarantined people with RT-PCR-confirmed SARS-CoV-2 infection, collecting clinical data, travel and contact history, and saliva at enrolment and daily nasopharyngeal throat swabs (NTS) for RT-PCR testing. We compared the natural history and transmission potential of asymptomatic and symptomatic individuals.

Results
Between March 10th and April 4th, 2020, 14,000 quarantined people were tested for SARS-CoV-2; 49 were positive. Of these, 30 participated in the study: 13(43%) never had symptoms and 17(57%) were symptomatic. 17(57%) participants acquired their infection outside Vietnam. Compared with symptomatic individuals, asymptomatic people were less likely to have detectable SARS-CoV-2 in NTS samples collected at enrolment (8/13 (62%) vs. 17/17 (100%) P=0.02). SARS-CoV-2 RNA was detected in 20/27 (74%) available saliva; 7/11 (64%) in the asymptomatic and 13/16 (81%) in the symptomatic group (P=0.56). Analysis of the probability of RT-PCR positivity showed asymptomatic participants had faster viral clearance than symptomatic participants (P<0.001 for difference over first 19 days). This difference was most pronounced during the first week of follow-up. Two of the asymptomatic individuals appeared to transmit the infection to up to four contacts.

Conclusions
Asymptomatic SARS-CoV-2 infection is common and can be detected by analysis of saliva or NTS. NTS viral loads fall faster in asymptomatic individuals, but they appear able to transmit the virus to others.

#asymptomatiques

APS - #Covid-19 : Les indicateurs ont beaucoup évolué en un mois (Dr Bousso)
▻http://aps.sn/actualites/societe/sante/article/covid-19-les-indicateurs-ont-beaucoup-evolue-en-un-mois-dr-bousso

Apparemment le #Sénégal fait beaucoup de tests chez les contacts de malades Covid-19, mais il n’est pas clair combien de sujets dépistés alors qu’ils sont asymptomatiques le demeurent au terme de leur isolement.

Sur l’aspect clinique, il a relevé que ‘’beaucoup se posent la question sur l’existence de la maladie puisque la majorité des cas sont #asymptomatiques avec 60,7% testés positifs qui ne présentent pas de symptômes’’. Près de la moitié des personnes qui sont testées positives ne présentent pas de signes cliniques.

#Espagne : un tiers des contaminés par le #coronavirus sont #asymptomatiques, selon une étude
▻https://www.sudouest.fr/2020/06/05/espagne-un-tiers-des-contamines-par-le-coronavirus-sont-asymptomatiques-sel

https://images.sudouest.fr/2020/06/05/5ed9e9ac66a4bd7b303d6efd/golden/5-21-de-la-population.jpg?v1

#sérologie #sars-cov2

What Iceland Can Teach the World About Minimizing the Coronavirus | Best Countries | US News
►https://www.usnews.com/news/best-countries/articles/2020-05-04/what-iceland-can-teach-the-world-about-minimizing-the-coronavirus

https://www.usnews.com/dims4/USNEWS/f5dc3df/2147483647/resize/1200x%3E/quality/85/?url=http%3A%2F%2Fmedia.beam.usnews.com%2F3b%2F80%2F92e5a5e04597862b22d1b0d5abd2%2F200501-editorial.streets.Getty.jpg

(Alors qu’il est rapporté que 50% des #SARS-Cov2 positifs sont asymptomatiques en #Islande)

Around half the people who tested positive in Iceland were asymptomatic. What percentage of them likely eventually developed symptoms? Also, did asymptomatic patients skew toward any one age group?

I think a very large percentage would have eventually developed symptoms. And within a few days, I will know exactly what that number is [#à_suivre]. They were evenly divided among the age groups.

#asymptomatiques