Lockdowns and Selection Pressure: A Modelling Study

Since COVID-19 was first identified in China in 2019, the SARS-CoV-2 virus has mutated and given rise to a large number of variants. A range of non-pharmaceutical interventions have been deployed against the virus in an effort to save lives and reduce pressure on health-care systems. These interventions may have favoured some variants over others. Despite this possibility, there has thus far been very little work investigating the impact of such interventions on the evolution of the virus. Using mathematical and computational models, we investigate the impact of a lockdown specifically, for the case in which two SARS-CoV-2 variants are circulating simultaneously in a population. We find that under certain conditions, lockdowns disrupt the competition between variants in such a way that highly transmissible variants with long infectious periods are selected for, ultimately leading to more cases overall than would have occurred without the lockdown, due to larger second waves of cases. These are the results of a modelling study and we do not claim to have found evidence of such unfavourable selection effects occurring in reality. On the other hand, our results are consistent with evolutionary theory and suggest that the selective effects of non-pharmaceutical interventions deserve greater scrutiny.