Superspreaders, asymptomatics and COVID‐19 elimination

Camilla Mattiuzzi and Giuseppe Lippi
Med J Aust 2021; 215 (3): 140-140.e1. || doi: 10.5694/mja2.51174
Published online: 2 August 2021

To the Editor: We read with interest the article by Kault,1 who carried out an analysis on superspreaders, asymptomatic cases, and coronavirus disease 2019 (COVID‐19) elimination. Although all efforts made for preventing or containing the COVID‐19 pandemic are certainly welcome, we raise doubts on some basic aspects used for constructing the prediction model and which do not seem to be evidence‐based.

In the risk model of COVID‐19 re‐emergence after release of restrictive measures (eg, lockdowns), Kault made some erroneous assumptions, including the fact that asymptomatic subjects may be as infectious as symptomatic patients with COVID‐19.1 This hypothesis seems to be contradicted by several lines of evidence. First, a meta‐analysis published in 2020 concluded that the rate of asymptomatic transmission of severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) infection is 35% lower compared with COVID‐19 patients with symptomatic illness.2 This has also been clearly explained in a seminal study showing that the viral load is the highest in concomitance with symptoms onset, so that the infectiousness of pre‐symptomatic or asymptomatic individuals is probably low.3 Notably, the impact of pre‐symptomatic SARS‐CoV‐2 transmission seems also rather limited, whereby the secondary attack rate was found to account for only 15% of all secondary COVID‐19 cases.4

A second aspect that needs to be highlighted is that presuming that 50% of SARS‐CoV‐2‐positive patients are asymptomatic may also be formally incorrect. Beside the fact that the asymptomatic SARS‐CoV‐2‐positive rate varies greatly depending on many genetic, demographic (ie, age, sex and ethnic origin) and even clinical (eg, time course of disease, comorbidities) variables, an analysis in the official database of the Italian National Institute of Health reveals, for example, that the rate of asymptomatic subjects with SARS‐CoV‐2 infection approximates 70%.5

Combined with lower infectiousness, the high prevalence of asymptomatic subjects bearing SARS‐CoV‐2 infection after release of restrictive practices (eg, lifting of lockdowns) would persuade us to conclude that the possible impact of asymptomatic superspreaders on SARS‐CoV‐2 transmission would be low and perhaps insufficient to influence or guide future policies aimed at restricting individual freedom.

  • Camilla Mattiuzzi1
  • Giuseppe Lippi2

  • 1 Service of Clinical Governance, Provincial Agency for Social and Sanitary Services, Trento, Italy
  • 2 Università degli Studi di Verona, Verona, Italy


Competing interests:

No relevant disclosures.


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