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

Francisco Perez-Reche; Norval Strachan

There are two main implications from the models which are directly relevant for policy in dealing with the outbreak. The first, involves the existence of a significant proportion of cases that are not tested and may act as silent carriers of the infection. We found that the predicted percentage of untested infected individuals may represent 50% to 80% of the cases in Germany, Hubei, Italy, Spain and the UK. The specific percentage depends on the country and we found the lowest proportion of unreported cases in Germany. Based on studies in Iceland 9 and the Diamond Princess cruise 7 , we conclude that asymptomatic infected individuals are likely to be the main contribution to the untested cases in all analysed outbreaks but a fraction of cases with mild symptoms are also likely to be untested. Even when unreported cases are taken into account, we estimate that less than 8% of the population would have been exposed to SARS-CoV-2 by 09/04/2020 in the analysed outbreaks. In policy terms, our results demonstrate that the current suppression strategies being employed in Germany, Hubei, Italy, Spain and the UK will not facilitate sufficient levels of herd immunity in the population that would control and eventually eradicate the virus. This leaves the risk of re-emergence of the virus once suppression strategies are lifted, similar to second waves of infection observed in 1918 influenza epidemics 34 . We predict, however, that partial relaxation of ongoing lockdowns could keep the number of daily deaths to potentially tolerable levels.