do & suspect others get confused with all the terms asymptomatic, atypical symptoms pre-symptomatic etc and i think this is used to push the head line and narrative
Coronavirus spread by people with no symptoms ‘appears to be rare,’ WHO official says
asymptomatic means a person who is infected but feels no symptoms. That person will at some point have a testable virus concentration in the throat and nasal cavity, and can spread that via droplets. About half of the people on the Diamond Princess who were tested positive had no symptoms at the time of testing. This also depends on which symptoms you watch out for; symptoms like fever or cough are each reported by fewer than half of the cases in Germany.
An "asymptomatic case" is a person who tests positive for the virus, but never reports symptoms.
pre-symptomatic is a person who is infected and later has symptoms; obviously, this can only be determined in hindsight. Studies have shown that the virus concentration in the throat and nasal cavity is decreasing from the first symptomatic day on, so researchers assume the peak of infectiousness is actually close to onset of symptoms, or shortly before; and that individuals are infectious 1-2 days before the onset of symptoms. Every symptomatic case has a pre-symptomatic period.
Common sense says that if you have the virus in your throat and nasal cavity, you will emit droplets/aerosols while breathing or speaking (or singing), so you can potentially infect people near you. That's why public health response adresses asymptomatic and presymptomatic transmission. For example, in the CDC's "best estimate" scenario for (hypothetical) unmitigated spread, 35% of the infected are asymptomatic, and ~60% of individual transmissions occur from asymptomatic or pre-symptomatic individuals; we have discussed this at
https://www.metabunk.org/threads/coronavirus-statistics-cases-mortality-vs-flu.11154/post-239340 .
Now let's look at the WHO quote in context; the WHO streams all of their press briefings on youtube and publishes transcripts the next day.
Source: https://m.youtube.com/watch?v=dZoIOyiZnt8&t=31m47s
00:31:47
TJ Thank you. Now we will go to Emma Farge from Reuters. Hello, Emma.
EM Yes, good afternoon. It's a question about asymptomatic transmission, if I may. I know that the WHO's previously said there're no documented cases of this. We had a story out of Singapore today saying that at least half of the new cases they're seeing have no symptoms and I'm wondering whether it's possible that this has a bigger role than the WHO initially thought in propagating the pandemic and what the policy implications of that might be.
MK [Maria van Kerkhove] I could start and then perhaps Mike would like to supplement. There're a couple of things in the question that you just asked. One is the number of cases that are being reported as asymptomatic. We hear from a number of countries that x number or x percentage of them are reported as not having symptoms or that they are in their pre-symptomatic phase which means it's a few days before they actually develop severe symptoms.
00:32:53
In a number of countries when we go back and we discuss with them, one, how are these asymptomatic cases being identified, many of them are being identified through contact tracing, which is what we want to see, that you have a known case, you find your contacts, they're already in quarantine hopefully and some of them are tested. Then you pick up people who may have asymptomatic or no symptoms or even mild symptoms.
The other thing we're finding is that when we go back and say, how many of them were truly asymptomatic we find out that many have really mild disease, they're not - quote, unquote - COVID symptoms meaning they may not have developed fever yet, they may not have had a significant cough or they may not have shortness of breath but some may have mild disease.
Having said that, we do know that there can be people that are truly asymptomatic and PCR-positive.
The second part of your question is what proportion of asymptomatic individuals actually transmit.
The way that we look at that is we look at - these individuals need to be followed carefully over the course of when they're detected and looking at secondary transmission.
00:34:04
We have a number of reports from countries who are doing very detailed contact tracing. They're following asymptomatic cases, they're following contacts and they're not finding secondary transmission onward. It's very rare and much of that is not published in the literature.
From the papers that are published there's one that came out from Singapore looking at a long-term care facility. There are some household transmission studies where you follow individuals over time and you look at the proportion of those that transmit onwards.
We are constantly looking at this data and we're trying to get more information from countries to truly answer this question. It still appears to be rare that an asymptomatic individual actually transmits onward.
00:34:48
What we really want to be focused on is following the symptomatic cases. If we followed all of the symptomatic cases - because we know that this is a respiratory pathogen, it passes from an individual through infectious droplets - if we followed all of the symptomatic cases, isolated those cases, followed the contacts and quarantined those contacts we would drastically reduce...
I would love to be able to give a proportion of how much transmission we would actually stop but it would be a drastic reduction in transmission. If we could focus on that I think we would do very, very well in terms of suppressing transmission.
But from the data we have it still seems to be rare that an asymptomatic actually transmits onward to a secondary individual.
The first consideration is, where does the data come from and what does it mean? Asymptomatic cases are mainly found through contact tracing; these people are typically asked to self-isolate, and so they will not usually pass the disease on.
Contact tracing also involves investigating how an individual got infected, finding an epidemiological link. If someone in a care home develops Covid-19, you need to find out who they got it from, because that determines who else might be infected. In these types of investigations, asymptomatic cases rarely turn up.
It also depends on where you draw the line: if you only accept fever, cough, shortness of breath as symptoms, you're going to label more cases as asymptomatic than if you also look at minor symptoms, e.g. soreness of throat or loss of taste or smell.
The second consideration (and the basis for the reporter's question) is, how many asymptomatic cases do we have in the population, and what role do they play epidemiologically? Some studies have suggested huge numbers of undetected (and presumably asymptomatic) infections.
The problem with that is that the WHO have advocated contact tracing and isolation as a containment strategy from the start. If 80% of the infections was asymptomatic, then you could only ever stop 20% of the spread by tracing individuals with symptoms. The only way to stop the rest would be social/physical distancing. But that's not what happens.
I live in Germany, and our county health offices always do contact tracing in epidemics (unless overwhelmed by big outbreaks, but we have a federal task force of contact tracers now that can help out). We have been re-opening the country last month, and in all states case numbers are still steady or declining. This indicates that contact tracing is working, and that we don't have widespread asymptomatic transmission.
This indicates that asymptomatic transmission plays a minor role, not a major role, in spreading the epidemic, and that the public health advice to invest in contact tracing still holds up. Note that pre-symptomatic infections still get traced; if an individual develops symptoms, they get asked who they were in contact with before they developed symptoms, and these contacts get notified, asked to self-isolate, and tested (depending on capacity).
Is this a "twist"? No.
WHO advice has always been to trace contacts. China has done that in Wuhan, deploying 1800 contact tracers (or 1800 teams, I've heard both), and deployed a restrictive app to automatically isolate contacts and monitor compliance.
But if you have a region with no contact tracing capability, or if the existing contact tracers are overwhelmed due to widespread community transmission, lockdown is your only option to stop the spread. Having sufficient contact tracing available (plenty enough personnel and few enough cases) is one of the criteria for re-opening, e.g. in New York state. Germany assumes a county will fail to trace effectively with >50 cases per week per 100 000 inhabitants. (I have been asssuming that a region with >10% positive tests is failing to test enough contacts.)
So, the worse prepared you are, the more you need to lock down. This is the reason why lockdowns are frequently the measure of first resort, and once the population has learned to distance, and testing and tracing capabilities have been built up, lockdowns can be lifted. IF you had a country that taught its population distancing early in their spread, and was well-prepared to trace contacts, it might mitigate the epidemic without lockdowns (Sweden!); that doesn't mean all countries were in a situation to do that. It all depends on how well a country was prepared for a pandemic in general, and how well it used the warning time (most countries had at least a month from the WHO's declaration of a "public health emergency of international concern" in late January) to ramp up testing capacity, organize contact tracing, and manage hospital capacity. Politics and government decide this.
So, the actual twist is: if a country was well prepared for a pandemic, executed its pandemic plans flawlessly, and had a population that took the pandemic seriously and followed distancing recommendations, it could avoid the lockdowns. On the other hand, Covid-19-denial causes lockdowns.
The conspiracy theory is that infections are everywhere and either are normal ("just a common cold that we notice because we can test for it") or will go away on their own ("we already have herd immunity"); both has been disproven by the mortality data and the serological surveys. Reports of large numbers of asymptomatic cases support the CT view, the WHO statement does not, therefore, the WHO statement needs to be discredited by the conspiracy theorists, therefore "twist"!
But there is no twist, it's all consistent with past communications.
P.S.:
New Zealand did eliminate the virus (for now) without vaccines (and so did Wuhan). Stopping vaccine research assumes that all countries can pull this off, but data shows not all regions do as well as New Zealand; and it assumes the virus will not re-emerge from its animal reservoir that we still haven't found.