This work consists of a systematic review of published works, following all the standards for this type of study. It aims to answer two specific questions:

(1) How many people are completely asymptomatic after SARS-CoV-2 infection?

(2) Since it has been reported that viral load can be as high in an asymptomatic person as in a symptomatic person, is the risk of transmission to others the same?

The authors draw two conclusions:

(1) The rate of true asymptomatics may be between 14-50%.

(2) Asymptomatic people have a lower risk of transmission than pre-symptomatic or symptomatic people.

These data confirm observations already made by other studies. As the authors themselves point out, one of the limitations of this work is that it is based on data published up to July 2021, which means that, for example, it does not assess whether the new variants (delta, omicron) change these conclusions. Nor is there a review of how these data change if we include vaccination as a factor that can certainly change the conclusions. 

In any case, if we have learned anything from this virus, it is that transmission from asymptomatic and presymptomatic people is one of the decisive factors that has contributed to the global spread of this virus and to the pandemic situation we are still in. The data from this study may be useful for public health services to implement pharmacological and non-pharmacological measures to curb the transmission of the virus in certain contexts.

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