Delta-plus is a subvariant of delta, which has been shown to be more transmissible than earlier forms of SARS-CoV-2. Delta-plus’ spike-protein mutation appears to allow it to bind more easily to lung cells, making it a more effective respiratory virus. Here’s a link: https://www.baptisthealth.com/connect-learn/covid19/covid19-resources/covid-19-variants/delta-variant#:~:text=Delta%2Dplus%20is%20a%20subvariant,a%20more%20effective%20respiratory%20virus.