COVID-19 Update 18: When are patients really infectious?

Individuals are infectious with COVID-19 when they’re shedding the virus, which means that the virus replicates in the cells of their upper or lower respiratory tract. In this video, we will examine published articles discussing viral shedding, the incubation period (mean incubation period was 5.2 days) and the serial interval, by examining the results of 77 COVID-19 transmission pairs.

The study found that infectiousness starts 2.3 days before symptom onset. That patients are most infectious 0.7 days before symptom onset.They also found that 44% of infectiousness or infections occurred in the pre-symptomatic phase making it difficult to track.

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Links for reference:

More updates by Dr. Wiesbauer:
COVID-19 Update 1: How to tell if a pandemic is likely to occur or not–R0 and the serial interval:
COVID-19 Update 2: How to stop an epidemic – Herd immunity:
COVID-19 Update 3: Symptoms of COVID-19:
COVID-19 Update 4: Clinical characteristics of COVID-19:
COVID-19 Update 5: Estimating case fatality rates for COVID-19:
COVID-19 Update 6: Seasonality: will COVID-19 go away in the summer?:
COVID-19 Update 7: This is probably the most important picture of the whole Coronavirus-epidemic:
COVID-19 Update 8: Zinc and chloroquine for the treatment of COVID-19?:
COVID-19 Update 9: Hydroxychloroquine and azithromycin for the treatment of COVID-19–Review of study by Didier Raoult:
COVID-19 Update 10: Is COVID-19 an airborne disease? Will we all need to wear face-masks against SARS-CoV-2?
COVID-19 Update 11: How exactly the coronavirus becomes airborne.
COVID-19 Update 12: Attack rates of COVID-19 depend on face-to-face time spent with infected persons:

COVID-19 Update 13: Randomized Controlled Trial of Hydroxychloroquine in Patients with COVID-19:

COVID-19 Update 14: Are children contributing to the spread of COVID-19?

COVID-19 Update 15: Can we disinfect and reuse N95 masks?:

COVID-19 Update 16: Effectiveness of surgical masks for prevention

COVID-19 Update 17: How an app can get us out of lockdown

Useful resources:
For checking daily developments of cases, deaths and more:

Other useful resources:
Journal Watch:

New England Journal of Medicine:

Github collaboration:




Speaker: Franz Wiesbauer, MD MPH
Internist & Founder at Medmastery

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Please Note: Medmastery’s videos, medical lectures, medical illustrations, and medical animations are for medical education and exam preparation purposes, and not intended to replace recommendations by your doctor or health care provider.


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22 responses to COVID-19 Update 18: When are patients really infectious?

  1. Hi may you please review the viral shedding and transmissible again. I feel I learn more after you explain it. I believed the reference you used might have as update as the authors made corrections about the graph and stats

  2. You have to be realistic about apps that violate people's privacy. How about home $1 antigen paper strip test that people can do daily and detect viral shedding hours after onset? This test exist. It's low sensitivity allows detection of people who have a lot of virus shedding, meaning being actually infectious. The low sensitivity is it's advantage. That would stop pandemic on it's track. FDA doesn't want to allow it. You know why? Because of low sensitivity. FDA is ruled by lawyers, not scientists.

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  4. The scientist who invented the PCR (Polymerase Chain Reaction) test kit was Kary B. Mullis. This technology is what they use today to test for the so-called coronavirus, said to be the cause of a disease which the health authorities such as the World Health Organizations (WHO) vaguely and inconsistently defined or identified.
    According to Mullis himself, PCR cannot be totally and should never be used as a tool in the diagnosis of infectious diseases.
    PCR is really a manufacturing technique. You start with a small amount of DNA and on each cycle the amount doubles, which doesn’t sound like that much, but if you double 30 times, you get approximately a billion times more material than you started with. So as a manufacturing technique, it’s great.
    I’m sad that he isn’t here to defend his manufacturing technique. Kary did not invent a test. He invented a very powerful manufacturing technique that is being abused. What are the best applications for PCR? Not medical diagnostics. He knew that and he always said that.”
    “You have to have a whopping amount of any organism to cause symptoms. Huge amounts of it. You don’t start with testing; you start with listening to the lungs. I’m skeptical that a PCR test is ever true. It’s a great scientific research tool. It’s a horrible tool for clinical medicine. 30% of your infected cells have been killed before you show symptoms. By the time you show symptoms…the dead cells are generating the symptoms”
    PCR for diagnosis is a big problem. When you have to amplify it these huge numbers of time, it’s going to generate massive amounts of false positives. Again, I’m skeptical that a PCR test is ever true.”
    The CDC and FDA both admit the COVID19 test kits suffer from false positives and false negatives. They just fail to tell you those rates. But others have revealed those rates. “the false-positive rate of positive results was 80.33%” and 85% false negative rate. The test kits don’t work. If the test kits don’t work, or are less reliable than a coin flip, then all the data on “who has it” is utterly meaningless and it’s all a total fraud and hoax. People are still dying, but from the same illness as always: the flu. 
    They don’t do antibody tests. They do a thing called PCR testing, which basically takes a sample of your cells and amplifies any DNA to look for ‘viral sequences’, i.e. bits of non-human DNA that seem to match parts of a known viral genome.
    The problem is the test is known to be bullshit.
    It uses ‘amplification’ which means taking a very very tiny amount of DNA and growing it exponentially until it can be analysed. Obviously any minute contaminations in the sample will also be amplified leading to potentially gross errors of discovery.
    Secondly, it’s only looking for partial viral sequences, not whole genomes, so identifying a single pathogen is next to impossible even if you ignore the other issues.
    All these Mickey Mouse test kits being sent out to hospitals do at best is tell the analysts you have some viral DNA in your cells. Which most of us do, most of the time. It may tell you the viral sequence is related to a specific type of virus – say the huge family of coronavirus. But that’s all.
    The idea these kits can isolate a specific virus like covid-19 is utter bullshit.
    And that’s not even getting into the other issue – viral load.
    If you remember the PCR works by amplifying minute amounts of DNA. It therefore is useless at telling you how much virus you may have.
    And that’s the only question that really matters when it comes to diagnosing illness. Like I said, everyone will have a few virus kicking round in their system at any time, and most will not cause illness because their quantities are too small. For a virus to sicken you, you need a lot of it, a massive amount of it. But PCR does not test viral load and therefore can’t determine if sufficient quantities are present to sicken you.
    If you feel sick and get a PCR test any random virus DNA might be identified even if they aren’t at all involved in your sickness. Leading to false diagnosis.
    And coronavirus are incredibly common. A large percentage of the world human population will have covi DNA in them in small quantities even if they are perfectly well or sick with some other pathogen.
    Do you see where this is going yet?
    If you want to create a totally false panic about a totally false pandemic – pick a coronavirus.
    They are incredibly common and there’s tons of them. A very high percentage of people sick by other means (flu, bacterial pneumonia, anything) will have a positive PCR test for covi even if you’re doing them properly and ruling out contamination, simply because covis are so common.
    There are hundreds of thousands of flu and pneumonia victims in hospitals throughout the world at any one time.
    All you need to do is select the sickest of these in a single location – say Wuhan – administer PCR tests to them and claim anyone showing viral sequences similar to a corona virus (which will inevitably be quite a few) is suffering from a ‘new’ disease.
    Since you already selected the sickest flu cases a fairly high proportion of your sample will go on to die.
    You can then say this ‘new’ virus has a CFR (case fatality rate) higher than the flu and use this to infuse more concern and do more tests which will of course produce more ‘cases’, which expands the testing, which produces yet more ‘cases’ and so on and so on.
    Before long you have your ‘pandemic’, and all you have done is use a simple test kit trick to convert the worst flu and pneumonia cases into something new that doesn’t actually exist.
    Now just run the same scam in other countries. Making sure to keep the fear message running high so that people will feel panicky and less able to think critically.
    Your only problem is going to be that – due to the fact there is no actual new deadly pathogen but just regular sick people you are mislabelling – your case numbers, and especially your deaths, are going to be way too low for a real new deadly virus pandemic.
    But you can stop people pointing this out in several ways.
    1. You can claim this is just the beginning and more deaths are imminent. Use this as an excuse to quarantine everyone and then claim the quarantine prevented the expected millions of dead.
    2. You can tell people that ‘minimising’ the dangers is irresponsible and bully them into not talking about numbers.
    3. You can talk bullshittery about r0 (the number of people, on average, that one infected person will subsequently infect) numbers hoping to blind people with pseudoscience
    4. You can start testing well people (who of course will also likely have shreds of coronavirus DNA in them) and thus inflate your ‘case figures’ with ‘asymptomatic carriers’ (you will of course have to spin that to sound deadly even though any virologist knows the more symptomless cases you have the less deadly is your pathogen
    Take these simple steps and you can have your own entirely manufactured pandemic up and running in weeks.
    But why are you doing this people may ask.
    Lots of reasons. Fear is useful. And a population frightened into demanding protection will accept anything you do to ‘protect’ them, up to and including nailing them into their own houses.
    It can be a trial run for social control methods. To see how gullible populations are. To enforce more rigorous censorship. To inure people to shortage and uncertainty.
    All these things and others are reasons.
    But getting hung up on possible motive misses the point – that all the evidence points to this being the case.
    Everything I am seeing points at a fake manufactured pandemic. The low numbers and attempts to inflate them with scary anecdotes and bad science, the crazy overreaction in world governments, as if the reaction itself is the point. The ridiculous numbers of famous people ‘testing positive’.
    It could easily be done and it looks as if it is. In my view. But you must make up your own mind.
    I think many in the virology and epidemiology line would agree, but no one is going to risk their career right now saying so in public. They might as well jump off of a bridge.
    You can verify everything I have said about the PCR test

  5. As a statistic this sounds like an okay plan, but as a person, it sounds like it is not so much of a consolation that I have an app if I catch it but maybe a bonus for those who might get it from me. I don’t see this as a substitute for a lockdown or contact tracing. It is a thought experiment run with no friction but the real world obstacles, logistic, social, political, ethical, etc… makes this idea seem much less feasible or likely to be the home run the video presents it to be.

  6. Why everyone should not wear a mask…I see nothing good coming from 320 million people…untrained in how to handle a Bio-hazard as a contaminated face mask would be …Better to have people cough into their elbow and wash their hands all the time…

  7. the new reports below show that this is not an Chinese conronavirus, cuz this coronavirus was detected in many places before the outbreak in China. unlike other countries putting corona-virus in to Flu section, China actually discovered it.

    1) Covid-19 virus was found in the sewage in spain march 2019

    2) "Earliest coronavirus case in the USA?" Mayor of Belville, New Jersey, Michael Melham says he has the virus antibodies in Nov 2019. He didn't visit China before this date.

    3) French scientists traced possible Covid 19 case back to Nov 2019.

    4) Italy have found traces of the new coronavirus in wastewater collected from Milan and Turin in December 2019.

  8. Thanks! I have a follow up question: I heard a person has a latency period, where they are not contagious for 24-48 hours after being exposed to the virus. Is this true? I understand you can calculate a certain amt of time before symptoms, but can you calculate infectiousness from the time you are exposed to enough virus. Thanks!

  9. Lots of graphs and explanation… but by an Internal medicine doctor… not a virologist. There is a reason infectious disease is a specialized medical profession and Ill opt for their input and daily focus with the ever changing discoveries of this virus

  10. Personal bookmark
    2:20 Transmission pairs
    7:06 infectiousness starts 2.3 days before symptom onset, most infectious on 0.7 days before symptom onset, and almost no infectiousness on seven days after symptom onset

  11. Digital tracing is both too much and too little. It's too much because it includes in the tracking list contacts that are so brief and casual they are unlikely to lead to an infection. It's too little in the sense that someone who rode an elevator might infect someone who also rides it fifteen minutes later even though they never got within a mile of one another. The contacts that matter are the ones that are extensive enough, say dining together, that people can remember them without digital tracking. That's where the effort should be devoted. It's also ridiculous to assume that the data could remain anonymous when it really matters. If a dictator took over, within days the contract tracing could included the names of who met who.

  12. I don't believe you can predict the inherently unpredictable viral transmission that is covid19. The app is great for statistics and a thesis but not in time for stopping a plague.

  13. This is interesting but now we see all this panick is oberblown.

    On you can find the number of cases, death rates etc. nicely for most countries.
    And the most interesting is death age distribution.

    And there you find that the average age of corona deaths is around 80 years.
    So its time to stop all this lockdown nonsense.

  14. 60 days of quarantine/ safedistancing, mask wearing and all other measures in place
    Should have already resolved (all seriously ill) and others would have recovered. And life can and should go on.


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