Amity Island
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Thanks Bruce! At Last! Someone else understands what I am talking about. Thank Goodness!
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How about this from a published report from the European Centre for Disease Prevention and Control? It clarifies the possibility of asymptomatic or presymptomatic transmission, and in the end kinda backs up my suggestion that there is simply no way of knowing what the proportion of cases is that are coming via asymptomatic/presymptomatic routes, because the data simply aren’t up to it. Infectiousness seems highest just as the symptoms emerge, but you can certainly be infectious before you get symptoms, and you may never get symptoms at all. The quality of observational data are poor, so if you are relying on that and ignoring the mathematical modelling that uses Covid’s similarities with flu behaviour, then you don’t leave yourself much to work with, and definitive statements like ‘very rare’ seem a little more like (expert) opinion than evidence-based to me?
Ive added emphasis:
Role of asymptomatic and pre-symptomatic individuals
Asymptomatic infection at time of laboratory confirmation has been reported from many settings [8,29-34]. Some of these cases developed some symptoms at a later stage of infection [35,36]. In a recent review, the proportion of positive cases that remained asymptomatic was estimated at 16%, with a range from 6 to 41% [37]. In another systematic review, the pooled proportion of asymptomatic cases at time of testing was 25% [38]. A majority of these cases developed symptoms later on, with only 8.4% of the cases remaining asymptomatic throughout the follow-up period [38]. There are also reports of asymptomatic cases with laboratory-confirmed viral shedding in respiratory and gastrointestinal samples [35,39,40]. Similar viral loads in asymptomatic versus symptomatic cases have been reported, indicating the potential of virus transmission from asymptomatic patients [41].
Asymptomatic transmission (i.e. when the infector has no symptoms throughout the course of the disease), is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias [38,42]. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers for the growth of the COVID-19 pandemic [43,44].
Although transmission from asymptomatic carriers has been reported [45,46], the risk of transmission from pre-symptomatic or symptomatic patients is considered to be higher. Viral RNA shedding is higher at the time of symptom onset and declines after days or weeks [13].
Pre-symptomatic transmission (i.e. when the infector develops symptoms after transmitting the virus to another person) has been reported [34,47,48]. Exposure of secondary cases occurred 1–3 days before the source patient developed symptoms [48]. It has been inferred through modelling that, in the presence of control measures, pre-symptomatic transmission contributed to 48% and 62% of transmissions in Singapore and China, respectively [49]. Pre-symptomatic transmission was deemed likely based on a shorter serial interval of COVID-19 (4.0 to 4.6 days) than the mean incubation period (five days) [50].
Major uncertainties remain with regard to the influence of pre-symptomatic transmission on the overall transmission dynamics of the pandemic because the evidence on transmission from asymptomatic cases from case reports is suboptimal.
www.ecdc.europa.eu
There may well be studies that say the opposite, of course... this was just the first one I found! 🙂
Ive added emphasis:
Role of asymptomatic and pre-symptomatic individuals
Asymptomatic infection at time of laboratory confirmation has been reported from many settings [8,29-34]. Some of these cases developed some symptoms at a later stage of infection [35,36]. In a recent review, the proportion of positive cases that remained asymptomatic was estimated at 16%, with a range from 6 to 41% [37]. In another systematic review, the pooled proportion of asymptomatic cases at time of testing was 25% [38]. A majority of these cases developed symptoms later on, with only 8.4% of the cases remaining asymptomatic throughout the follow-up period [38]. There are also reports of asymptomatic cases with laboratory-confirmed viral shedding in respiratory and gastrointestinal samples [35,39,40]. Similar viral loads in asymptomatic versus symptomatic cases have been reported, indicating the potential of virus transmission from asymptomatic patients [41].
Asymptomatic transmission (i.e. when the infector has no symptoms throughout the course of the disease), is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias [38,42]. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers for the growth of the COVID-19 pandemic [43,44].
Although transmission from asymptomatic carriers has been reported [45,46], the risk of transmission from pre-symptomatic or symptomatic patients is considered to be higher. Viral RNA shedding is higher at the time of symptom onset and declines after days or weeks [13].
Pre-symptomatic transmission (i.e. when the infector develops symptoms after transmitting the virus to another person) has been reported [34,47,48]. Exposure of secondary cases occurred 1–3 days before the source patient developed symptoms [48]. It has been inferred through modelling that, in the presence of control measures, pre-symptomatic transmission contributed to 48% and 62% of transmissions in Singapore and China, respectively [49]. Pre-symptomatic transmission was deemed likely based on a shorter serial interval of COVID-19 (4.0 to 4.6 days) than the mean incubation period (five days) [50].
Major uncertainties remain with regard to the influence of pre-symptomatic transmission on the overall transmission dynamics of the pandemic because the evidence on transmission from asymptomatic cases from case reports is suboptimal.
Factsheet for health professionals on COVID-19
Factsheet on the COVID-19 pathogen, surveillance, clinical features, epidemiology, transmission, case management, and public health control measures.
There may well be studies that say the opposite, of course... this was just the first one I found! 🙂
Amity Island
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Mike,How about this from a published report from the European Centre for Disease Prevention and Control? It clarifies the possibility of asymptomatic or presymptomatic transmission, and in the end kinda backs up my suggestion that there is simply no way of knowing what the proportion of cases is that are coming via asymptomatic/presymptomatic routes, because the data simply aren’t up to it. Infectiousness seems highest just as the symptoms emerge, but you can certainly be infectious before you get symptoms, and you may never get symptoms at all. The quality of observational data are poor, so if you are relying on that and ignoring the mathematical modelling that uses Covid’s similarities with flu behaviour, then you don’t leave yourself much to work with, and definitive statements like ‘very rare’ seem a little more like (expert) opinion than evidence-based to me?
Ive added emphasis:
Role of asymptomatic and pre-symptomatic individuals
Asymptomatic infection at time of laboratory confirmation has been reported from many settings [8,29-34]. Some of these cases developed some symptoms at a later stage of infection [35,36]. In a recent review, the proportion of positive cases that remained asymptomatic was estimated at 16%, with a range from 6 to 41% [37]. In another systematic review, the pooled proportion of asymptomatic cases at time of testing was 25% [38]. A majority of these cases developed symptoms later on, with only 8.4% of the cases remaining asymptomatic throughout the follow-up period [38]. There are also reports of asymptomatic cases with laboratory-confirmed viral shedding in respiratory and gastrointestinal samples [35,39,40]. Similar viral loads in asymptomatic versus symptomatic cases have been reported, indicating the potential of virus transmission from asymptomatic patients [41].
Asymptomatic transmission (i.e. when the infector has no symptoms throughout the course of the disease), is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias [38,42]. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers for the growth of the COVID-19 pandemic [43,44].
Although transmission from asymptomatic carriers has been reported [45,46], the risk of transmission from pre-symptomatic or symptomatic patients is considered to be higher. Viral RNA shedding is higher at the time of symptom onset and declines after days or weeks [13].
Pre-symptomatic transmission (i.e. when the infector develops symptoms after transmitting the virus to another person) has been reported [34,47,48]. Exposure of secondary cases occurred 1–3 days before the source patient developed symptoms [48]. It has been inferred through modelling that, in the presence of control measures, pre-symptomatic transmission contributed to 48% and 62% of transmissions in Singapore and China, respectively [49]. Pre-symptomatic transmission was deemed likely based on a shorter serial interval of COVID-19 (4.0 to 4.6 days) than the mean incubation period (five days) [50].
Major uncertainties remain with regard to the influence of pre-symptomatic transmission on the overall transmission dynamics of the pandemic because the evidence on transmission from asymptomatic cases from case reports is suboptimal.
Factsheet for health professionals on COVID-19
Factsheet on the COVID-19 pathogen, surveillance, clinical features, epidemiology, transmission, case management, and public health control measures.
There may well be studies that say the opposite, of course... this was just the first one I found! 🙂
It gave me a cough just reading that! lol all this talk of covid19.
I'll have a look and get back.
Amity Island
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Hi Mike,How about this from a published report from the European Centre for Disease Prevention and Control? It clarifies the possibility of asymptomatic or presymptomatic transmission, and in the end kinda backs up my suggestion that there is simply no way of knowing what the proportion of cases is that are coming via asymptomatic/presymptomatic routes, because the data simply aren’t up to it. Infectiousness seems highest just as the symptoms emerge, but you can certainly be infectious before you get symptoms, and you may never get symptoms at all. The quality of observational data are poor, so if you are relying on that and ignoring the mathematical modelling that uses Covid’s similarities with flu behaviour, then you don’t leave yourself much to work with, and definitive statements like ‘very rare’ seem a little more like (expert) opinion than evidence-based to me?
Ive added emphasis:
Role of asymptomatic and pre-symptomatic individuals
Asymptomatic infection at time of laboratory confirmation has been reported from many settings [8,29-34]. Some of these cases developed some symptoms at a later stage of infection [35,36]. In a recent review, the proportion of positive cases that remained asymptomatic was estimated at 16%, with a range from 6 to 41% [37]. In another systematic review, the pooled proportion of asymptomatic cases at time of testing was 25% [38]. A majority of these cases developed symptoms later on, with only 8.4% of the cases remaining asymptomatic throughout the follow-up period [38]. There are also reports of asymptomatic cases with laboratory-confirmed viral shedding in respiratory and gastrointestinal samples [35,39,40]. Similar viral loads in asymptomatic versus symptomatic cases have been reported, indicating the potential of virus transmission from asymptomatic patients [41].
Asymptomatic transmission (i.e. when the infector has no symptoms throughout the course of the disease), is difficult to quantify. Available data, mainly derived from observational studies, vary in quality and seem to be prone to publication bias [38,42]. Mathematical modelling studies (not peer-reviewed) have suggested that asymptomatic individuals might be major drivers for the growth of the COVID-19 pandemic [43,44].
Although transmission from asymptomatic carriers has been reported [45,46], the risk of transmission from pre-symptomatic or symptomatic patients is considered to be higher. Viral RNA shedding is higher at the time of symptom onset and declines after days or weeks [13].
Pre-symptomatic transmission (i.e. when the infector develops symptoms after transmitting the virus to another person) has been reported [34,47,48]. Exposure of secondary cases occurred 1–3 days before the source patient developed symptoms [48]. It has been inferred through modelling that, in the presence of control measures, pre-symptomatic transmission contributed to 48% and 62% of transmissions in Singapore and China, respectively [49]. Pre-symptomatic transmission was deemed likely based on a shorter serial interval of COVID-19 (4.0 to 4.6 days) than the mean incubation period (five days) [50].
Major uncertainties remain with regard to the influence of pre-symptomatic transmission on the overall transmission dynamics of the pandemic because the evidence on transmission from asymptomatic cases from case reports is suboptimal.
Factsheet for health professionals on COVID-19
Factsheet on the COVID-19 pathogen, surveillance, clinical features, epidemiology, transmission, case management, and public health control measures.
There may well be studies that say the opposite, of course... this was just the first one I found! 🙂
Thanks for all the info.
Firstly, we can certainly eliminate the "pre-symptomatic" data, as that was never mentioned in Dr Maria Van Kerkhove's statement "asymptomatic transmission appears to be very rare".
Regarding her statement, I can only conclude that in her role as COVID19 lead for the World Health Organisation, she too has seen all the types of studies you've referenced, yet still came to her conclusion that "asymptomatic transmission is very rare".
As we know, she did add an additional statement the next day which talks about a computer model, which I think it would be safe to say, that at the moment this type of "evidence" is not actual evidence and the reliability of models is limited because there just isn't enough data input to make a decent model.
As I said before, you have to put trust in the people trusted and relied upon to draw a professional conclusion from what evidence they have seen. I certainly wouldn't like to nor do I have the qualifications, experience or knowledge to be able to challenge that opinion and I'm not aware of anyone else with her credentials and experience to challenge her either.
That's me done on this subject...I'm not here to defend someone I've never met.
She said it not me and i'm not sure why I am being challenged on a statement made by someone else?
I'm not saying she's right or wrong, I only referred to her statement as it's from a reliable source, not some conspiracy nut.
If anyone feels so strongly about her statement being wrong, you could write to the WHO and provide evidence to the contrary.
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Only because you asked another member which of the facts you had presented it was that they had issues with, and Dr Kerkhove‘s comment was one of the things you had posted that made me think, “well that doesn’t make sense to me... if you can‘t and aren’t measuring it - how can you make an assessment of how large or small an effect it is having”
Well in which case it seems we are down to semantics... I am far less interested in the precise sandboxing of asymptomatic spreaders vs people spreading coronavirus with no symptoms who then develop them later. Pragmatically I am more interested in people behaving in such a way as to limit their ability to spread coronavirus even if they don’t have any symptoms, because the science shows that not having symptoms *today* doesnt mean that you haven’t got, and aren’t spreading covid... so it's better if everyone to takes reasonable precautions.
But yes... I think the conversation has run its course! 🙂
Amity Island
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On 13 May, the Elsevier Public Health Emergency Collection published a report in the US National Library of Medicine titled ‘A study on infectivity of asymptomatic SARS-CoV-2 carriers’. Written by Chinese doctors working in Guangdong Provincial People’s Hospital, this had been able to trace and test 455 individuals — 35 hospital patients, 196 family members and 224 hospital staff — who had been brought into contact with an asymptomatic patient admitted to hospital in January and subsequently found to be infected with SARs-CoV-2. They concluded:
‘It is debatable whether asymptomatic COVID-19 virus carriers are contagious. The median contact time for patients was four days and that for family members was five days. No severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections was detected in 455 contacts by nucleic acid test.
‘In summary, all the 455 contacts were excluded from SARS-CoV-2 infection and we conclude that the infectivity of some asymptomatic SARS-CoV-2 carriers might be weak. This finding implies that there is no need to worry unduly for asymptomatic or mild patients during the ongoing COVID-19 pandemic.
‘Under the development of epidemic circumstance, more and more public concern is on the increasing number of asymptomatic or mild patients hid in the community. However, combined with our results and the defense measures currently completed, we hope such worries are misplaced.’
Another study on ‘Modes of contact and risk of transmission in COVID-19 among close contacts’, published on 26 March, tested 305 contacts of 8 asymptomatic cases and found 1 instance of secondary transmission. A study on ‘Coronavirus Disease Outbreak in Call Center, South Korea’, published on 23 April, found 4 asymptomatic cases out of 97 infections, and, again, none of their 17 household contacts acquired secondary infections. A study on ‘Contact Tracing Assessment of COVID-19 Transmission Dynamics in Taiwan and Risk at Different Exposure Periods Before and After Symptom Onset’, published on 1 May, reported that ‘none of the 9 asymptomatic case patients transmitted a secondary case’ to their 91 close contacts. A study on ‘SARS-CoV-2 transmission in different settings: Analysis of cases and close contacts from the Tablighi cluster in Brunei Darussalam’, published on 8 May, reported that among 9 cases with 691 contacts there were 15 incidence of secondary transmission. A summary review of medical studies ‘Estimating the extent of asymptomatic COVID-19 and its potential for community transmission: systematic review and meta-analysis’, published on 10 May, found that, among these four studies providing direct evidence of asymptomatic transmission, the rate of infection among 1,091 study cases ranged from none to 2.2 per cent. And a study reporting ‘No evidence of secondary transmission of COVID-19 from children attending school in Ireland, 2020’, published on 28 May, found that an asymptomatic schoolchild with SARs-CoV-2 who came into close or casual contact with 180 people resulted in ‘no confirmed cases of COVID-19’.
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Robin
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And meanwhile, the virus is moving the goalposts...
Does this mean that any studies which involve data from early Chinese infections will prove not to hold true for the virus as it now is in most Western countries, I wonder? Time will tell.
Coronavirus: Are mutations making it more infectious?
While there have been thousands of changes to the virus only one is seen as possibly altering its behaviour.
www.bbc.co.uk
Amity Island
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Hi Robin,And meanwhile, the virus is moving the goalposts...
Does this mean that any studies which involve data from early Chinese infections will prove not to hold true for the virus as it now is in most Western countries, I wonder? Time will tell.Coronavirus: Are mutations making it more infectious?
While there have been thousands of changes to the virus only one is seen as possibly altering its behaviour.www.bbc.co.uk
That does make me wonder about how we'll ever find a vaccine if the virus keeps mutating?
Robin
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So far, the Oxford vaccine team say they are working on disabling a certain spike on the virus that doesn’t seem to be one that has or (hopefully) will mutate. Fingers crossed...
mikeyB
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The spike on the virus is common to all coronaviruses, so this vaccine is more of a generic coronavirus vaccine. It may help stop getting a cold - around 20% of the 100 or so viruses that cause colds are coronaviruses. It needs the spike to lock onto cells, so it’s unlikely to change by mutation - it would stop the virus from working properly.
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