A pair of peer-reviewed articles on the efficacy of Project ImPACT with infant siblings at-risk for ASD was recently published in Autism by Paul Yoder, Wendy Stone, and Sarah Edmunds.
Yoder, P., Stone, W., & Edmunds, S. (in press). Parent utilization of ImPACT intervention strategies is a mediator of proximal then distal social communication outcomes in younger siblings of children with ASD. Autism https://journals.sagepub.com/doi/abs/10.1177/1362361320946883
Yoder, P., Stone, W., & Edmunds, S. (in press). For which younger siblings of children with autism spectrum disorder does parent-mediated intervention work? Autism. https://journals.sagepub.com/doi/abs/10.1177/1362361320943373