Symptomless transmission of COVID-19 silently drives viral spread and is key to ending the pandemic, write Angela L. Rasmussen and Saskia V. Popescu in this Perspective. However, "[u]ntil there is widespread implementation of robust surveillance and epidemiological measures that allow us to put out these smokeless fires," they say, "the COVID-19 pandemic cannot be fully extinguished." Determining the true transmission capability of asymptomatic and presymptomatic cases is inherently complex. Among the reasons, the prevalence of symptomless cases is not precisely established, and, too, determining their risk for secondary transmission has been hindered by a reliance on symptom-based testing and a lack of surveillance testing. In the population, data on asymptomatic and presymptomatic cases who had close contacts but did not result in transmission are limited. As well, the minimum infectious dose required for transmission is not known and likely varies depending on individual exposure and susceptibility. Finally, from a public health point of view, the emphasis on the degree of contagiousness rather than the knowledge that people without symptoms are generally contagious detracts from the perceived threat that asymptomatic and presymptomatic infections pose, as well as the need for interventions. "Academic debates about the frequency of different transmission routes reframe exposure risk reduction as a dichotomy rather than a spectrum," the authors add, "confusing rather than informing guidance." They say that rather than targeting transmission by either inhalation or contact, infection prevention efforts should focus instead on the additive nature of risk reduction and the need for continued vigilance in community-based infection prevention measures.
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Science