Modelling the effect of virulent variants with SIR

We study the effect of an emerging virus mutation on the evolution of an epidemic, inspired by the appearanceof the delta variant of SARS-CoV-2. We show that if the new variant is markedly more infective than theexisting ones the epidemic can resurge immediately. The vaccination of the population plays a crucial role inthe evolution of the epidemic. When the older (and more vulnerable) layers of the population are protected,the new infections concern mainly younger people, resulting into fewer hospitalisations and a reduced stress onthe health system. We study also the effects of vacations, partially effective vaccines and vaccination strategiesbased on epidemic-awareness. An important finding concerns vaccination deniers: their atttude may lead to aprolonged wave of epidemic and an increased number of hospital admissions