Why Is Rare Asymptomatic COVID Transmission a Bad Thing?

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The World Health Organization (WHO) sparked outrage this week when a scientist simply relayed what they were observing, that asymptomatic transmission of COVID-19 was rare.  Why? Let’s explore.

What Was Said

Maria Van Kerkhove, who is an infectious disease epidemiologist and the technical lead of their COVID-19 response team as well as the head of emerging diseases unit at WHO, stated in a press conference that asymptomatic transmission of COVID-19 was “very rare”. She came to that conclusion by reviewing data that the WHO had received from countries that had performed extensive contact tracing. This caused the media to freak out.

The actual statement was, “From the data we have, it still seems to be rare that an asymptomatic person actually transmits onward to a secondary individual. 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 is very rare — and much of that is not published in the literature. 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 ” She then discussed that if countries just aggressively isolate the sick, transmission rates would drop.

This of course is FANTASTIC news, as this means that economies can reopen more aggressively and just screen for sick people!

However, this set off a firestorm in the media:

  • Are asymptomatic people spreading the coronavirus? A WHO official’s words spark confusion, debate – Washington Post (11)
  • Coronavirus update: Global infections climb above 7.1 million as health experts question WHO statement on asymptomatic carriers – MarketWatch (12)

In fact, the media push back was so severe, that this poor scientist was forced to “walk back” this statement.

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Leaving the Media Fantasyland and Digging into What We Know

Let’s dig into what we actually know about asymptomatic transmission of COVID-19. Before we do, we have a few definitions. When someone transmits a viral disease to another person, they can either be:

  • Asymptomatic – no symptoms and none ever develop.
  • Presymptomatic – no symptoms when the transmission happens, but then the person gets sick later
  • Paucisymtomatic – Minimal symptoms when he spread happens and the patient never gets really sick
  • Symptomatic – Full symptoms when the disease is transmitted to someone else

There are different types of transmission as well:

  • Close contact – i.e. through family members living in the same house
  • Community spread – the disease is spread from one person in the community to another

So what do we know about situations where COVID-19 patients aren’t fully sick when they transmit the disease to the community at large?  I reviewed the first 40 papers listed in the U.S. National Library of Medicine.

Asymptomatic Spread Among Close Contacts

Let’s dig into this data. One Chinese paper discusses a small cluster of cases where asymptomatic and paucisymptomatic transmission occurred, but only among close contacts (parent to child) (1). Multiple other published accounts of asymptomatic transmission were again to family members (3-5,7-9). There is also a case report of a COVID-19 positive, Italian man evacuated from China with 55 other citizens. This situation demonstrated no spread from this paucisymptomatic patient to the other travelers on the same plane (who wore face masks and washed their hands) (2).

Community Spread by Asymptomatic Patients

A Chinese published report documents a pre-symptomatic teenager who infected other teens at a gathering while asymptomatic, then the teen developed symptoms (6). This is the only paper I could find that documented asymptomatic spread among non-family members.

How About the Notorious Washington State Choir Event?

If you recall, the media made a big deal about a Washington state choir where COVID-19 was spread at a practice event. Near as I can tell, this hasn’t been published in a medical journal. However, reading the CDC account, one person at one of the practices was symptomatic which accounted for all but one case of dozens (10). Hence, this was not asymptomatic spread, but symptomatic spread. This is also called a “super-spreader” event which is a known phenomenon in pandemics, but thankfully rare.

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Why Was the Media So Upset by this WHO Comment?

Any normal human being hearing an expert who has reviewed advanced contact tracing data state that asymptomatic transmission of COVID-19 was rare, would jump up and down, and breathe a sigh of relief. However, the media went into overdrive to discredit this expert. Why? The published data clearly supports what she said. While we may still need to know more, the fact that about 10 published papers and whatever other information this woman reviewed shows that this is rare, is a good thing.

As I always tell my kids, please take what the media reports with a big grain of salt. Right now, they have epic traffic to websites allowing them to maximize sales of eyeballs to advertisers. The more they can keep the public afraid, the more eyeballs there are to sell. It’s really that simple.

Why would university talking heads be complicit in all of this? In fact, many were quoted throwing this poor scientist at WHO under the bus. First, we don’t know what the commenters in these stories actually said, meaning the reporters could have taken any snippet of their comments and went with the one that supported the narrative. However, you also need to realize that the attention on this virus has bolstered many university public health departments. Hence, the fact that there is likely very rare asymptomatic spread is also not good for this crowd.

The upshot? Science and medicine are no longer driving the COVID-19 policy bus, instead the fear-mongering media has taken over the driver’s seat. This is NOT good.



(1)  Xiao-Lin J, et al. Transmission Potential of Asymptomatic and Paucisymptomatic Severe Acute Respiratory Syndrome Coronavirus 2 Infections: A 3-Family Cluster Study in China, The Journal of Infectious Diseases, , jiaa206, https://doi.org/10.1093/infdis/jiaa206

(2) Nicastri E, D’Abramo A, Faggioni G, et al. Coronavirus disease (COVID-19) in a paucisymptomatic patient: epidemiological and clinical challenge in settings with limited community transmission, Italy, February 2020. Euro Surveill. 2020;25(11):2000230. doi:10.2807/1560-7917.ES.2020.25.11.2000230

(3) Bai Y, Yao L, Wei T, et al. Presumed Asymptomatic Carrier Transmission of COVID-19 [published online ahead of print, 2020 Feb 21]. JAMA. 2020;323(14):1406‐1407. doi:10.1001/jama.2020.2565

(4) Hu Z, Song C, Xu C, et al. Clinical characteristics of 24 asymptomatic infections with COVID-19 screened among close contacts in Nanjing, China. Sci China Life Sci. 2020;63(5):706‐711. doi:10.1007/s11427-020-1661-4

(5) Yu X, Yang R. COVID-19 transmission through asymptomatic carriers is a challenge to containment [published online ahead of print, 2020 Apr 4]. Influenza Other Respir Viruses. 2020;10.1111/irv.12743. doi:10.1111/irv.12743

(6) Huang L, Zhang X, Zhang X, et al. Rapid asymptomatic transmission of COVID-19 during the incubation period demonstrating strong infectivity in a cluster of youngsters aged 16-23 years outside Wuhan and characteristics of young patients with COVID-19: A prospective contact-tracing study. J Infect. 2020;80(6):e1‐e13. doi:10.1016/j.jinf.2020.03.006

(7) Qian G, Yang N, Ma AHY, et al. A COVID-19 Transmission within a family cluster by presymptomatic infectors in China [published online ahead of print, 2020 Mar 23]. Clin Infect Dis. 2020;ciaa316. doi:10.1093/cid/ciaa316

(8) Ye F, Xu S, Rong Z, et al. Delivery of infection from asymptomatic carriers of COVID-19 in a familial cluster. Int J Infect Dis. 2020;94:133‐138. doi:10.1016/j.ijid.2020.03.042

(9) Zhang J, Tian S, Lou J, Chen Y. Familial cluster of COVID-19 infection from an asymptomatic. Crit Care. 2020;24(1):119. Published 2020 Mar 27. doi:10.1186/s13054-020-2817-7

(10) The Centers for Disease Control and Prevention. Morbidity and Mortality Weekly Report (MMWR). High SARS-CoV-2 Attack Rate Following Exposure at a Choir Practice — Skagit County, Washington, March 2020. https://www.cdc.gov/mmwr/volumes/69/wr/mm6919e6.htm

(11) The Washington Post. Are asymptomatic people spreading the coronavirus? A WHO official’s words spark confusion, debate. https://www.washingtonpost.com/health/2020/06/09/asymptomatic-coronavirus-spread-who/ Accessed 6/10/20.

(12) MarketWatch. Coronavirus update: Global infections climb above 7.2 million as health experts question WHO statement on asymptomatic carriers. https://www.marketwatch.com/story/coronavirus-update-global-infections-climb-above-71-million-as-health-experts-question-who-statement-on-asymptomatic-carriers-2020-06-09 Accessed 6/10/20.

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