COVID19 update, June 14, 2020: avoiding the Three C’s of Transmission; most asymptomatic cases remain asymptomatic

Busy workday, so just some quick updates:

(1) (hat tip: Masgramondou): Are Technica: “Just 10-20% of cases are behind 80% of transmission” 

Benjamin Cowling, a Hong Kong-based epidemiologist and biostatistics expert, agrees. Cowling and colleagues recently studied transmission in Hong Kong, finding superspreading events drove local transmission. In a recent op-ed, he and a colleague argue that public health policies aimed at stopping the pandemic should focus on stopping superspreading.

“The epidemic’s growth can be controlled with tactics far less disruptive, socially and economically, than the extended lockdowns or other extreme forms of social distancing that much of the world has experienced over the past few months,” the researchers wrote

In an email to Ars, Cowling fleshed out this idea a bit, noting that “measures that specifically target superspreading are those that reduce or prevent large gatherings of people,” such as those to reduce the density of people in schools and workplaces.

Measures not specifically targeted to superspreading, he noted, “are those like asking everybody to stay at home as much as they can, despite many workplaces and social settings not being places that superspreading could occur.”

In the op-ed, Cowling noted that Japan—which has been relatively successful at managing the pandemic—has employed an anti-superspreading policy called [“the Three Cs Of Transmission”]: Avoid (1) Closed spaces with poor ventilation, (2) Crowded places, and (3) Close-contact settings, such as close-range conversations. The risk for superspreading is highest in situations with all three Cs.

[…]Cowling and his colleagues’ analysis has been posted online but has not yet been peer-reviewed or published in a scientific journal. But, they note, their findings from Hong Kong aren’t unique. For instance, a study published in the Lancet in April, which looked at transmission of SARS-CoV-2 in Shenzhen, China, found that just around 9 percent of cases accounted for 80 percent of transmission. And a modeling study from researchers in London likewise found that just about 10 percent of cases may account for 80 percent of transmission.

Read the whole thing.

(2) via Instapundit, this report by UPI quoting this letter to the New England Journal of Medicine from a Japanese team:

The outbreak of coronavirus disease 2019 (Covid-19) on the cruise ship Diamond Princess led to 712 persons being infected with SARS-CoV-2 among the 3711 passengers and crew members, and 410 (58%) of these infected persons were asymptomatic at the time of testing[….] A total of 96 persons infected with SARS-CoV-2 who were asymptomatic at the time of testing, along with their 32 cabinmates who tested negative on the ship, were transferred from the Diamond Princess to a hospital in central Japan between February 19 and February 26 for continued observation. Clinical signs and symptoms of Covid-19 subsequently developed in 11 of these 96 persons, a median of 4 days (interquartile range, 3 to 5; range, 3 to 7) after the first positive polymerase-chain-reaction (PCR) test, which meant that they had been presymptomatic rather than asymptomatic.

[…] The group of persons with asymptomatic SARS-CoV-2 infection consisted of 58 passengers and 32 crew members, with median age of 59.5 years (interquartile range, 36 to 68; range, 9 to 77). A total of 24 of these persons (27%) had coexisting medical conditions, including hypertension (in 20%) and diabetes (9%). The first PCR test at the hospital was performed a mean of 6 days after the initial positive PCR test on the ship. The median number of days between the first positive PCR test (either on the ship or at the hospital) and the first of the two serial negative PCR tests was 9 days (interquartile range, 6 to 11; range, 3 to 21), and the cumulative percentages of persons with resolution of infection 8 and 15 days after the first positive PCR test were 48% and 90%, respectively. The risk of delayed resolution of infection increased with increasing age.

In this cohort, the majority of asymptomatically infected persons remained asymptomatic throughout the course of the infection. The time to the resolution of infection increased with increasing age.


(3) UnHerd: so where did the virus really come from? Dogmatic answers do not behoove a scientist, as the writer rightly argues. On the other hand, extraordinary claims (e.g., a genetically engineered virus) require extraordinary proof. Either way, we need all the evidence we can get. Read the whole article.

This is in the realm of speculation, but I’ve been wondering: what if, after the outbreak began, local officials panicked thinking this may be a human-“improved” virus that had escaped from the WiV, then calmed down once it became clear it was “only” another novel coronavirus. That would explain some of the skittish behavior in the very beginning, the destruction of samples,…  

ADDENDUM: yes, public health experts are undermining themselves by U-turning on recommendations for political expedience. 

And Insta snarks “nothing to see here, move along”: Parts of Beijing locked down due to fresh virus cluster

ADDENDUM 2: Israeli public health expert on what we might face in the winter 

COVID-19: interesting data from Korea and from the Diamond Princess

One of the first countries to deal with the epidemic was South Korea. Unlike China, South Korea is a fairly transparent society and data published by the Korean CDC (Center for Disease Control) can be more or less taken at face value.

A progress report is published every day on their website: here is today’s edition.

The most interesting part of the report is Table 5, which I am reproducing as a screenshot below:

Table 5 from the Korean CDC report, March 18, 2020

Let’s have a good look at this. Preliminary remark: Korea started a massive testing (according to Table 1 in the same report, nearly 300,000 people have been tested, at a current rate of 10,000 a day) and tracking program early, leveraging all available tech data — privacy concerns be darned.

Observation 1: overall mortality is 1 (one) percent. Still one percent too much, to be sure. But considerably lower than what has been reported from some other places — I suspect because of undertesting.

Observation 2: mortality in the 0-29 age bracket is nil — not one death out of 2,867 patients.

Observation 3: in the 30-49 age bracket, just two (2) deaths out of 2,044 patients, or about 0.1%. Only above 50 does mortality start rising, over 60 in a worrisome fashion. (Not coincidentally, so do comorbidities/pre-existing conditions. I would love to see the statistics broken down between otherwise healthy people and those with chronic cardiovascular/pulmonary/immunity/diabetes problems, or cancer patients. Hypertension is apparently another major risk factor.)

Observation 4: Note the interesting “gender gap”. Men (1.39%) have nearly twice the mortality of women (0.75%). I asked friends on Facebook familiar with South Korea, and they told me over half of men smoke, compared to fewer than five percent of women.

Now what can we expect for older people who are otherwise healthy? Chinese data (caveat lector) suggest overall mortality for patients without comorbidities may be about one-third the overall statistic.

And then there is the uncertainty factor of how many people are asymptomatic virus carriers. This is impossible to ascertain without a much more massive testing program (and this isn’t a test you can quickly do with a strip!), but I have seen estimates from 5-7 carriers for each overt disease case.

But the Diamond Princess cruise ship offers an interesting insight. It had nearly 4,000 people on board—many of them in risk groups. (Somebody who used to perform aboard cruise ships quipped that passengers are mostly “the newlywed and the nearly dead” ;)) You’d expect these packed together on a ship in quarantine to be all infecting each others. And yet… 4,061 passengers and crew were examined, on board what effectively became an unintentional virus incubator. Only 712 contracted the virus (about 17.5%), of which 334 asymptomatic (8.2% of the total), leaving 378 (9.3% of the total) ill. Only 7 people died (1.85% of those ill, or 0.17% of all passengers and crew examined), all of them age 70 or older. (Remember, the passenger population is skewed toward the elderly.)

One might treat Diamond Princess stats as an upper limit (since spreading in even dense urban areas will never be as efficient as on a cruise ship) and South Korea as what can be achieved with agile and efficient tracking and containment measures.

Meanwhile, a frantic search for both vaccines and drugs continues. One track that may yield results earliest is the repurposing of existing drugs following off-label testing, since safety and “therapeutic interval” testing have already been done for their original approval. I have mentioned a promising remdesivir trial and I see increasing reports that chloroquine (which has been used for decades as an antimalarial) may interferewith the virus lifecycle. (See e.g.,

Be well, stay healthy, be prepared, and remember:

[L]et me assert my firm belief that the only thing we have to fear is fear itself — nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance.

FDR, inaugural address (1933)

UPDATE: via Behind The Black,

(1) an article in SCIENCE about South Korea and how it got a “wake-up call” in 2015 when a businessman brought back MERS from the Middle East

(2) a lengthy analysis of the Diamond Princess data
(3) are there 6 asymptomatic or “too mild to notice” cases for each clinical case?


UPDATE 2: computational biochemistry pioneer Michael Levitt (2013 Nobel Prize in Chemistry shared with Arieh Warshel and Martin Karplus) sounds an optimistic note based on what he knows. His comments start off with Israel (he divides his time between Weizmann and Stanford) but then go on to the rest of the world.