Why Pharmacies Should Worry About Presymptomatic, Asymptomatic COVID-19

The CDC has provided information on why asymptomatic/presymptomatic transmission of the novel coronavirus is not just theoretical. Find out what a new literature review determined about the risk and which new questions it raises about COVID-19 patients who transmit the infection before they develop symptoms or, in some cases, never develop symptoms at all.

ATLANTA – Presymptomatic or asymptomatic COVID-19 is of significant concern to pharmacies and other businesses that serve a steady stream of customers seeking essential products. That is why the national Centers for Disease Control and Prevention recently advised that nearly everyone at drugstores were masks at all times, as well as other social-distancing guidelines.

Questions have been raised, however, whether transmission without symptoms is simply theoretical. A new literature review from the CDC helps provide some answers and finds that the risk very real.


“Recent epidemiologic, virologic, and modeling reports support the possibility of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission from persons who are presymptomatic (SARS-CoV-2 detected before symptom onset) or asymptomatic (SARS-CoV-2 detected but symptoms never develop),” according to public health researchers. “SARS-CoV-2 transmission in the absence of symptoms reinforces the value of measures that prevent the spread of SARS-CoV-2 by infected persons who may not exhibit illness despite being infectious.”

The review was launched, according to the authors, because it remains unknown how commonly asymptomatic and symptomatic SARS-CoV-2 infection occur and also whether asymptomatic SARS-CoV-2 infection confers protective immunity.

For the rapid literature review, the authors searched the literature in PubMed for articles that were published from Jan.1 through April 2, 2020 and were related to presymptomatic or asymptomatic SARS-CoV-2 transmission. Essentially, the search was looking for literature published until the time CDC made policy changes recommending community cloth face coverings and universal masking in healthcare facilities.

“All primary patients experienced distinct periods of initial exposure and presymptomatic close contact with secondary patients who had no other known exposure risks,” according to the CDC report. “The incubation periods for presymptomatic primary patients with distinct exposures ranged from three to 11 days; for presymptomatic primary patients with travel history to an area with active transmission, the time from last exposure to symptom onset ranged from >2 to >9 days.”

In addition the authors discuss four reports that documented the presence of SARS-CoV-2 RNA with lower viral loads in samples collected from people for whom symptoms of COVID-19 never developed, as well as two reports describing specimens with low RT-PCR Ct values among presymptomatic and asymptomatic residents of a nursing home identified as part of the same outbreak investigation.

The CDC study states that the findings have several implications, including:

  • The case-fatality rate for COVID-19 may be lower than currently estimated ratios if asymptomatic SARS-CoV-2 infections are included.
  • Transmission while asymptomatic reinforces the value of community interventions to slow the transmission of COVID-19.
  • Asymptomatic transmission enhances the need to scale up the capacity for widespread testing and thorough contact tracing to detect asymptomatic infections, interrupt undetected transmission chains, and further bend the curve downward.

The article suggests that that the incidence of asymptomatic compared with symptomatic SARS-CoV-2 infection needs to be determined. It also points to the need to quantify the effectiveness of public health interventions designed to reduce transmission from asymptomatic or presymptomatic patients and to new innovations in disease detection and prevention (beyond exhaustive contact tracing, mass testing, and isolation of asymptomatic contacts) in response.

The authors also call for more research on whether those with asymptomatic or mild SARS-CoV-2 infection develop full or partial immunity and “if it is possible to be immune from reinfection but still asymptomatically transmit SARS-CoV-2 while in a carrier state.”

“This information will be crucial for projecting the anticipated course of the pandemic and the potential for SARS-CoV-2 resurgence if immunity wanes,” according to the article. “Information about immunity is also valuable for healthcare and other critical infrastructure workers for whom rates of exposure, and thereby asymptomatic infection, may be higher and who therefore warrant data-informed guidance on how to safely return to work. The answers to these questions will be crucial for guiding the gradual relaxing of community interventions, resuming the normal functions of society, and recovering from the COVID-19 pandemic.”

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