https://api.elsevier.com/content/article/pii/S0893965921000987doi:10.1016/j.aml.2021.1071971-s2.0-S089396592100098710.1016/j.aml.2021.107197S0893-9659(21)00098-7Vaccination in a two-group epidemic model Applied Mathematics LettersJournal089396592021-09-30September 20210falsefalse