We believe that a high percentage of covid-19 infections could be due to the presence of false negative (FN) individuals on rapid swabs. To support this hypothesis and quantify their number, we performed simulations using Bayes' rule and various assumptions about the sensitivity, specificity of swabs and prevalence of infection. Imagining FNs in liberty, we then calculated the probability of encountering them in groups of people with a typical number of habitual sites, such as: bus, supermarket, theatre, etc. The probability of encountering FN from rapid tests was more than 3 times higher (345% change) that reported by the RT-PCR test.