Importance of untested infectious individuals for the suppression of COVID-19 epidemics

Francisco Perez-Reche; Norval Strachan

Optimising interventions to mitigate or suppress the burden of COVID-19 remains a pressing global challenge due to significant uncertainties regarding the transmissibility of SARS-CoV-2 and other factors such as possibly a large proportion of undocumented infections as well as political, social and economic considerations 5, 6 . Underreporting of infections may depend on the testing ability of different countries and the presence of asymptomatic infected individuals [7] [8] [9] . There is no consensus on the proportion of unreported cases and their potential impact on the spread of SARS-CoV-2. For instance, a World Health Organization report in February suggested that "the proportion of truly asymptomatic infections is unclear but appears to be relatively rare and does not appear to be a major driver of transmission" 10 . Studies testing for SARS-CoV-2 infection in both symptomatic and asymptomatic individuals [7] [8] [9] , however, suggest that asymptomatic carriers can represent 50% or more of the cases. In many countries that mostly test individuals when they have symptoms, unreported infections are likely to include at least most of the asymptomatic individuals or those with mild symptoms. Such individuals can act as silent carriers for SARS-CoV-2 and have been suggested as a key factor promoting the rapid spread of the virus 11 , similar to what has been observed in other infectious diseases 12 . On the positive side, if recovery from infection leads to immunity, one could hope that untested positive individuals could significantly contribute to the build-up of herd immunity in the population 13, 14 . It is not clear to what extent this could be the case. The importance of silent carriers on interventions for mitigation and suppression 15 of the infection is not clear either.