• Attack rates amongst household members of outpatients with confirmed #COVID-19 in Bergen, Norway : A case-ascertained study - ScienceDirect

    Attack rates = sujets asymptomatiques et symptomatiques

    Seuls les symptomatiques ont eu un PCR, mais tous ont eu une sérologie.

    La spécificité du test sérologique n’est pas discutée.

    #SARS-CoV-2 specific antibodies were measured in sera collected 6–8 weeks after index patient nasopharyngeal testing to define household attack rates.

    The overall attack rate was 45% (95% CI 38–53) assessed by serology, and 47% when also including seronegative RT-PCR positives. Serology identified a higher number of infected household members than RT-PCR [(44/70 vs. 32/70)],
    Attack rates were equally high in children (48%) and young adults (42%). The attack rates was 16% in asymptomatic household members [8/49] and 42% in RT-PCR negative contacts [16/38]. [...]

    Serological assays provide more sensitive and robust estimates of household attack rates than RT-PCR. Children are equally susceptible to infection as young adults . Negative RT-PCR or lack of symptoms are not sufficient to rule out infection in household members.

    #sérologie #séroconversion #asymptomatiques #enfants #transmission #anticorps

  • Dire que le #vaccin est efficace aussi contre les formes #asymptomatiques, est-ce à dire qu’il n’y a pas trace du virus dans l’organisme ?

    Eric Topol sur Twitter : “Not exactly. You can be vaccinated and carry the virus (carrier). But if the viral load is so low you can’t transmit (not a transmitter) spread is blocked and we move onto the pandemic exit ramp.” / Twitter

  • Efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine against SARS-CoV-2 variant of concern 202012/01 (B.1.1.7) : an exploratory analysis of a randomised controlled trial - The Lancet

    (Variant britannique)

    L’étude est analysée dans un éditorial de la même revue, qui met en avant deux constatations occultées dans le résumé de ladite étude :

    1) le vaccin pourrait être nettement moins efficace contre les formes #asymptomatiques du variant britannique (nombre de malades trop faible pour tirer des conclusions fermes)

    2) les intervalles de confiance, trop larges, ne permettent pas de tirer des conclusions solides concernant les formes symptomatiques.

    Although based on small case numbers, a larger difference in efficacy was observed for #SARS-CoV-2 infections with no or unreported symptoms (28·9% [–77·1 to 71·4] for B.1.1.7 and 69·7% [33·0 to 86·3] for other #variants).


    Given the wide CIs in these exploratory analyses, no firm conclusions can be drawn on the precise clinical efficacy against the B.1.1.7 variant and, importantly, how this efficacy compares with efficacy against the original circulating variants. However, the results point towards lower efficacy, which also seems consistent with the nine-times reduction in neutralising activity against the B.1.1.7 #variant compared with non-B.1.1.7 variants in the serum samples from vaccinees in this study.

    #vaccins #vaccination

  • Antibody Response After SARS-CoV-2 Infection and Implications for Immunity : A Rapid Living Review : Annals of Internal Medicine : Vol 0, No 0

    Revue de la littérature sur la #sérologie après une infection SARS-CoV-2 et les conséquences sur l’immunité

    4-6% des infectés restent séronégatifs (11% des asymptomatiques). La présence d’anticorps semble donc corrélée à la présence de symptômes mais aussi à leur sévérité : aucune des personnes hospitalisées ne s’est révélée séronégative.

    Les études sur les infections survenant après un test sérologique montrent que les séropositifs développent beaucoup moins d’infection par la suite ; mais la quasi-totalité des cas étudiés concernaient des personnes sans PCR préalable .

    To synthesize evidence on the prevalence, levels, and durability of detectable antibodies after #SARS-CoV-2 infection and whether antibodies to SARS-CoV-2 confer natural immunity.

    Lack of an Antibody Response

    Nearly all studies found that a certain proportion of patients with SARS-CoV-2 infection confirmed by RT-PCR did not have detectable antibodies. For example, in an Icelandic seroprevalence study in which 489 recovered patients had antibody testing at 2 time points (once ≥3 weeks after diagnosis and again ≥1 month after that), 19 (4%) had negative results for 2 pan-Ig immunoassays (29). Few studies evaluated whether patient factors and illness severity were associated with this finding. An exception is a U.S. study of 2547 frontline health care workers and first responders, which found that about 6% of participants remained seronegative 14 to 90 days after symptom onset (50). This result was strongly associated with disease severity and presence of symptoms. Although 11% of 308 asymptomatic patients did not develop antibodies, none of the 79 patients hospitalized for COVID-19 were seronegative.

    Role of Antibodies in Immunity Against Reinfection

    Studies in this review primarily aimed to estimate seroprevalence and characterize the antibody response after SARS-CoV-2 infection and did not directly evaluate the association between antibodies and immunity. A retrospective study of 47 hospitalized patients in China with moderate to severe COVID-19 mentions a potential case of reinfection in 1 patient during the “convalescence stage” of the disease (77). Of note, the patient did not have detectable antibodies (either IgM or IgG) at follow-up 4 weeks after discharge, but the study does not provide more detail or describe how reinfection was determined. Otherwise, we did not identify any studies of persons with SARS-CoV-2 infection diagnosed via RT-PCR that directly linked the presence or absence of antibodies with incidence of reinfection. A Danish study is investigating immunity by following participants positive for SARS-CoV-2 antibodies at 1, 5, 10, and 20 years, but so far it has reported only initial antibody test results (35). Population seroprevalence studies, such as the Icelandic study discussed in the previous section, could provide insight into reinfection risk if study periods were extended and incidence of reinfection compared among participants with and without antibodies.

    We note that, in several recent studies of adults with known positive or negative SARS-CoV-2 serologies, antibody presence is associated with protective immunity. A prospective study following 12 541 health care workers in the United Kingdom for up to 31 weeks found that anti-spike IgG seropositivity at baseline was associated with lower risk for subsequent positive results on RT-PCR testing for SARS-CoV-2 (223 of 11 364 vs. 2 of 1265; adjusted incidence rate ratio, 0.11) (83, 84). Only 37% (466 of 1265) of the seropositive workers had a prior RT-PCR–confirmed infection. Two small retrospective studies also suggest that prior SARS-CoV-2 infection, as measured by positive antibody results, is associated with reduced risk for reinfection (85, 86). One of these studies described a SARS-CoV-2 outbreak among attendees and staff at a summer school retreat (85). Among 152 participants, 76% (n = 116) had confirmed or presumed SARS-CoV-2 infection, whereas none of the 24 persons who had documented seropositive results in the 3 months before the retreat developed symptoms. In another study, 3 participants who had positive neutralizing antibody results (and negative results on RT-PCR testing for SARS-CoV-2) before departing on a fishing vessel did not subsequently test positive for SARS-CoV-2 despite an outbreak affecting 85% (104 of 122) of the onboard population (86).

    #anticorps #immunité #réinfection #asymptomatiques

  • Some People Get Covid-19 and Never Feel a Thing: Why?

    Asymptomatic cases are not unique to Covid-19. They occur with the regular flu, and probably also featured in the 1918 pandemic, according to epidemiologist Neil Ferguson of Imperial College London. But scientists aren’t sure why certain people weather Covid-19 unscathed. “ That is a tremendous mystery at this point ,” says Donald Thea, an infectious disease expert at Boston University’s School of Public Health.


    These experts are learning that the human body may not always wage an all-out war on viruses and other pathogens. It may also be capable of accommodating an infection, sometimes so seamlessly that no symptoms emerge. This phenomenon, known as disease tolerance , is well-known in plants but has only been documented in animals within the last 15 years.


    At least 90 percent of those infected with the tuberculosis bacterium don’t get sick.


    “With things like Covid, I think it’s going to be very parallel to TB, where you have this Goldilocks situation,” says Andrew Olive, an immunologist at Michigan State University, “where you need that perfect amount of inflammation to control the virus and not damage the lungs.”

    Some of the key disease tolerance mechanisms scientists have identified aim to keep inflammation within that narrow window. For example, immune cells called alveolar macrophages in the lung suppress inflammation once the threat posed by the pathogen diminishes.


    Studies show that their lungs often display damage on CT scans , yet they are not struggling for breath (though it remains to be seen whether they will fully escape long-term impacts). Moreover, a small recent study suggests that asymptomatics mount a weaker immune response than the people who get sick — suggesting that mechanisms are at work that have nothing to do with fighting infection.

    “Why, if they have these abnormalities, are they healthy?” asks Ayres. “Potentially because they have disease tolerance mechanisms engaged. These are the people we need to study.”


    A 2018 experiment in Ayres’ lab offered proof of concept for that goal. The team gave a diarrhea-causing infection to mice in a lethal dose 50 trial, then compared tissue from the mice that died with those that survived, looking for differences. They discovered that the asymptomatic mice had utilized their iron stores to route extra glucose to the hungry bacteria, and that the pacified germs no longer posed a threat. The team subsequently turned this observation into a treatment. In further experiments, they administered iron supplements to the mice and all the animals survived, even when the pathogen dose was upped a thousandfold.

    #infection #asymptomatiques #immunité #tolérance

  • #SARS-CoV-2 #transmission without symptoms | Science

    Viral replication and symptom onset
    The titer of infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and the amount of viral RNA are generally lower in asymptomatic (A) than presymptomatic (Pre) #COVID-19. There is likely to be a threshold at which a person becomes contagious, but this is not known. In presymptomatic patients, symptoms usually begin when viral load peaks, so there is a period of infectiousness when a person has no symptoms.

    #asymptomatiques #pré-symptomatiques #contagiosité

  • Seroprevalence and humoral immune durability of anti-#SARS-CoV-2 antibodies in Wuhan, China : a longitudinal, population-level, cross-sectional study - The Lancet

    Étude longitudinale de la #séroprévalence des #anticorps anti-#SARS-CoV-2 à Wuhan

    #Sérologie positive chez 6,9% des personnes testées,

    – 82% des personnes séropositives n’avaient pas développé la maladie (ou plus probablement une partie de celles-ci ont eu des symptômes mineurs qui sont vite passés)

    – Les anticorps étaient protecteurs (neutralisant) chez 40% (60% des symptomatiques et 36% des #asymptomatiques)

    – Les taux d’anticorps neutralisant sont restés stables pendant au moins 9 mois, y compris chez les asymptomatiques.


  • Impact of the COVID-19 Vaccine on Asymptomatic Infection Among Patients Undergoing Pre-Procedural COVID-19 Molecular Screening | Clinical Infectious Diseases | Oxford Academic

    #COVID-19 : Les #vaccins à ARNm efficaces contre la #transmission #asymptomatique | santé log

    Cette étude de chercheurs de la Mayo Clinic Rochester met en exergue une autre qualité des vaccins anti-COVID à ARN messager (ARNm) : ils permettent de réduire considérablement le risque d’infection asymptomatique au COVID-19 et donc le risque de propagation « silencieuse » associé.

    #vaccination #sars-cov2

  • Early Release - Analysis of Asymptomatic and Presymptomatic Transmission in SARS-CoV-2 Outbreak, Germany, 2020 - Volume 27, Number 4—April 2021 - Emerging Infectious Diseases journal - CDC

    In this cluster of COVID-19 cases, little to no transmission occurred from asymptomatic case-patients [0 cas en fait]. Presymptomatic #transmission was more frequent [75%] than symptomatic transmission. The serial interval was short [incubation médiane : 4,3 jours] ; very short intervals occurred.


    In conclusion, our study suggests that asymptomatic cases are unlikely to contribute substantially to the spread of #SARS-CoV-2. #COVID-19 cases should be detected and managed early to quarantine close contacts immediately and prevent presymptomatic #transmissions.

    #asymptomatiques #asymptomatique

  • Dr Zoë Hyde sur Twitter : “Pre-print study (interpret carefully) of an outbreak in a childcare centre in Québec (17 cases in children and 4 in adults at the centre, plus 8 adult family members and 1 child sibling), showing asymptomatic children can readily transmit #SARS-CoV-2, proven by genome sequencing.” / Twitter

    #asymptomatiques #transmission #contagiosité #enfants

  • Assessment of Day-7 Postexposure Testing of Asymptomatic Contacts of #COVID-19 Patients to Evaluate Early Release from Quarantine — Vermont, May–November 2020 | MMWR

    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.

  • #SARS-CoV-2 #Transmission From People Without COVID-19 Symptoms | Infectious Diseases | JAMA Network Open | JAMA Network

    The baseline assumptions for the model were that peak infectiousness occurred at the median of symptom onset and that 30% of individuals with infection never develop symptoms and are 75% as infectious as those who do develop symptoms. Combined, these baseline assumptions imply that persons with infection who never develop symptoms may account for approximately 24% of all transmission. In this base case, 59% of all transmission came from asymptomatic transmission, comprising 35% from presymptomatic individuals and 24% from individuals who never develop symptoms. Under a broad range of values for each of these assumptions, at least 50% of new SARS-CoV-2 infections was estimated to have originated from exposure to individuals with infection but without symptoms.

    Conclusions and Relevance
    In this decision analytical model of multiple scenarios of proportions of asymptomatic individuals with COVID-19 and infectious periods, transmission from asymptomatic individuals was estimated to account for more than half of all transmissions. In addition to identification and isolation of persons with symptomatic COVID-19, effective control of spread will require reducing the risk of transmission from people with infection who do not have symptoms. These findings suggest that measures such as wearing masks, hand hygiene, social distancing, and strategic testing of people who are not ill will be foundational to slowing the spread of COVID-19 until safe and effective vaccines are available and widely used.


    • On savait que c’était majoritaire, ils se risquent à des estimations chiffrées. Ce qui peut aider à mieux faire piger ce point central à ces sceptiques qui croient ne croire que ce qu’ils voient (et regardent pas mal de vidéos déglinguantes comme on peut en trouver ici même ) : une majorité des contaminations est le fait de « porteurs sains » (au moins au moment où elles ont lieu), et avec lui l’autre aspect central : c’est le plus indiscernable, l’aérosolisation qui cause la majorité des contaminations. J’ai étoilé car je compte utiliser l’article de cette façon... (rien de glorieux, le côté pédago avec de la répétition - limite bourrage de crânes- des analogies, par exemple le VIH, et ce qu’il faut de variation pour par sombrer dans le désintérêt)

      Si il s’agit d’une lutte commune, encore faut-il que les (des) notions et contraintes de base soient connues. La compétence politique des n’importe qui en dépend. Nous en sommes loin.

      #contamination #porteurs_sains

  • #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

    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

    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


  • Post-lockdown #SARS-CoV-2 nucleic acid screening in nearly ten million residents of Wuhan, China

    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

    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.


  • What the data say about asymptomatic #COVID infections

    Définition : Au moins 7 jours de suivi sans symptômes
    20% des sujets infectés sont asymptomatiques ;
    contagieux mais moindre que les symptomatiques ;
    leur rôle dans la propagation n’est pas capital
    Leur charge virale est initialement aussi importante que les symptomatiques (d’où la nécessité des mesures barrière malgré tout) mais diminue plus rapidement.

    Research early in the pandemic suggested that the rate of asymptomatic infections could be as high as 81%. But a meta-analysis published last month1, which included 13 studies involving 21,708 people, calculated the rate of asymptomatic presentation to be 17%. The analysis defined asymptomatic people as those who showed none of the key COVID-19 symptoms during the entire follow-up period, and the authors included only studies that followed participants for at least seven days. Evidence suggests that most people develop symptoms in 7–13 days, says lead author Oyungerel Byambasuren, a biomedical researcher at the Institute for Evidence-Based Healthcare at Bond University in Gold Coast, Australia.

    Byambasuren’s review also found that asymptomatic individuals were 42% less likely to transmit the virus than symptomatic people.

    One reason that scientists want to know how frequently people without symptoms transmit the virus is because these infections largely go undetected. Testing in most countries is targeted at those with symptoms.

    As part of a large population study in Geneva, Switzerland, researchers modelled viral spread among people living together. In a manuscript posted on medRxiv this month2, they report that the risk of an asymptomatic person passing the virus to others in their home is about one-quarter of the risk of transmission from a symptomatic person.

    Although there is a lower risk of transmission from asymptomatic people, they might still present a significant public-health risk because they are more likely to be out in the community than isolated at home, says Andrew Azman, an infectious-disease epidemiologist at the Johns Hopkins Bloomberg School of Public Health in Baltimore, Maryland, who is based in Switzerland and was a co-author on the study. “The actual public-health burden of this massive pool of interacting ‘asymptomatics’ in the community probably suggests that a sizeable portion of transmission events are from asymptomatic transmissions,” he says.

    But other researchers disagree about the extent to which asymptomatic infections are contributing to community transmission. If the studies are correct in finding that asymptomatic people are a low transmission risk, “these people are not the secret drivers of this pandemic”, says Byambasuren. They “are not coughing or sneezing as much, they’re probably not contaminating as much surfaces as other people”.

    Muge Cevik, an infectious-disease researcher at the University of St Andrews, UK, points out that because most people are symptomatic, concentrating on identifying them will probably eliminate most transmission events.

    Viral dynamics

    To understand what is happening in people with no symptoms, Cevik and colleagues conducted a systematic review and meta-analysis3 of 79 studies on the viral dynamics and transmissibility of SARS-CoV-2, which is posted on social-sciences preprint server SSRN. Some studies showed that those without symptoms had similar initial viral loads — the number of viral particles present in a throat swab — when compared with people with symptoms. But asymptomatic people seem to clear the virus faster and are infectious for a shorter period.

    The immune systems of asymptomatic individuals might be able to neutralize the virus more rapidly, says Cevik. But that doesn’t mean these people have a stronger or more durable immune response — and there is evidence that people with severe COVID-19 have a more substantial and long-lasting neutralizing antibody response, she says.

    Although there is a now a better understanding of asymptomatic infections and transmission of COVID-19, Cevik says that asymptomatic people should continue to use measures that reduce viral spread, such as social distancing, hand hygiene and wearing a mask.


    1. Byambasuren, O. et al. J. Assoc. Med. Microbiol. Infect. Dis. Can. https://doi.org/10.3138/jammi-2020-0030 (2020).

    #asymptomatique #contagiosité

  • #Transmission of #SARS-COV-2 Infections in Households — Tennessee and Wisconsin, April–September 2020 | MMWR

    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


    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.


    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

    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

    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.

  • Saliva** or Nasopharyngeal Swab Specimens for Detection of #SARS-CoV-2 | NEJM

    Rapporté en français ci-dessous :

    Test de détection salivaire du SARS-Co V2 - Revue Médicale Suisse

    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.


    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 :

    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

    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

    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

    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

    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.


    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.