This strain is officially named AY.4.2 and transmits more easily than other variants of Covid-19.
Officials designated the strain as a ‘variant under investigation’ on October 20.
Scientists are still working out whether it is more transmissible, or whether there are other factors helping it spread.
Vaccines are proving as effective against Delta Plus as they are against other Delta variants, two separate studies have found.
The UK Health Security Agency (UKHSA) said: ‘There is no evidence of increased severity based on risk of hospitalisation or death.’
The Wellcome Sanger Institute, one of the research bodies that which works with the UKHSA, analysed more than 36,000 positive Covid-19 tests from the week to November 13.
These tests were studied in order to determine the proportion of cases which were the Delta Plus variant.
Here are the Delta Plus variant figures for Portsmouth, Gosport, Fareham, Havant, Chichester, Winchester and East Hampshire.