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Addressing Questions of the Asymptomatic Spread of COVID-19

On-Site Staff

June 10, 2020

Rates of asymptomatic transmission of the novel virus remains a varying trend. It is a controversial topic, and it requires daily monitoring of the evidence. Despite conflicting data, there is some data that everybody agrees on regarding asymptomatic spread.

Large organizations’ role in informing the public

Rapidly spreading COVID-19 infection rates prompted the World Health Organization (WHO) to declare a public health emergency at the beginning of 2020 and soon later name it pandemic. Since then, there have been many controversies regarding COVID-19 outbreaks observed worldwide. The general population relies on reputable organizations’ statements and daily news when looking for medical advice and recent research. The COVID-19 pandemic has surprised many in terms of the spread of the virus from person-to-person and keeps surprising them, thus conflicting information is available in the media. Reliance is due to many unknowns, including the unpredictable spread of the disease, confusing signs and symptoms, fragmented research, as well as changing positions of even the most reputable health care organizations. For example, the WHO in the recent statement mentioned by Forbes (1), suggested on June 8th that the spread of the disease from “asymptomatic” carriers is “very rare” (which sparked the discussion among health care experts), was corrected after just two days stating that the estimated rates of the asymptomatic spread remain around 40% of cases (2).

Asymptomatic versus Presymptomatic Presentation

There is a need to distinguish who is an “asymptomatic” carrier and who is infected but does not show symptoms yet, two different categories in the world of epidemiology. The asymptomatic patients can still be a source to propagate new outbreaks, as they have a viral load large enough to infect those around them, and they do not have symptoms and will never get symptoms (3). Dr. Fauci defined the pre-symptomatic spread as “the transmission of the virus by people who don't look or feel sick but will eventually get symptoms later” (4). The presymptomatic period is typically 3-5 days (5). They also can infect others without knowing it. Presymptomatic individuals are not easy to detect, and the prolonged incubation time of COVID-19 makes it a highly contagious disease. The epidemiology of asymptomatic presentation among different populations is still difficult to obtain. The percentage of asymptomatic cases ranges from 5% to 80%. There are more asymptomatic cases relative to symptomatic cases in children, previously healthy individuals, and usually fewer in elderly populations, including nursing home residents, but as stated previously, data is inconsistent (6).

Asymptomatic versus Symptomatic Presentation and Transmission

The length of transmitting the disease differs from symptomatic and asymptomatic carriers. Because individuals who present with respiratory symptoms are prone to sneezing and coughing, they can expel more causative organisms from the one organism and exposing others to it (2). The studies on asymptomatic individuals are challenging to conduct without random testing of large population samples, but evidence shows that 25% to 45% of infected people likely don't have symptoms (4) (40-45 % according to another study) (7). The idea of testing as many individuals as possible seems to be very promising, but it will come with a financial price.


Rates of asymptomatic transmission of the novel virus remains a varying trend (2). It is a controversial topic, and it requires daily monitoring of the evidence. Despite conflicting data, there is some data that everybody agrees on regarding asymptomatic spread. First, it is possible to spread the disease from those who are symptomatic, asymptomatic, or presymptomatic. Secondly, roughly half of the cases of COVID-19 are spread from people without symptoms. Therefore social isolation and wearing masks (restricting the spread of droplets), although it is a separate topic. Lastly, when talking about the asymptomatic spread, it is essential to think in terms of three categories: symptomatic, asymptomatic, mildly symptomatic, and pre-symptomatic (patient is infected, is spreading the virus to others and will develop symptoms later on up to 14 days) categories (7).

1. Perez M. WHO Says Asymptomatic Spread Of Coronavirus “Very Rare,” But Experts Raise Questions [Internet]. 2020 [cited 2020 Jun 10]. Available from:
2. Coronavirus: WHO retracts statement within a day that said asymptomatic COVID-19 carriers cannot spread infection. Here is an explainer [Internet]. WHO retracts its statement on asymptomatic carriers spreading COVID-19. 2020 [cited 2020 Jun 10]. Available from:
3. Ye F, Xu S, Rong Z, Xu R, Liu X, Deng P, et al. Delivery of infection from asymptomatic carriers of COVID-19 in a familial cluster. Int J Infect Dis. 2020 May;94:133–8.
4. Yan Holly. Fauci says the WHO’s comment on asymptomatic spread is wrong. Here’s the difference between asymptomatic and pre-symptomatic spread [Internet]. CNN. 2020. Available from:
5. Kenneth McIntosh. Coronavirus disease 2019 (COVID-19): Clinical features and diagnosis. In: UpToDate. Waltham, MA; 2020.
6. Carl Heneghan, Jon Brassey, Tom Jefferson. COVID-19: What proportion are asymptomatic? [Internet]. 2020 [cited 2020 Jun 10]. Available from:
7. Jeff Craven, Katie Lennon. Asymptomatic COVID-19 Spread Deemed “Rare,” WHO Says [Internet]. 2020 [cited 2020 Jun 10]. Available from:

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