LONDON (Reuters) – England’s new track and tracing system was able to contact two thirds of the people who tested positive for COVID-19 and were referred to it in its first week, and then succeeded in contacting 85% of their contacts to ask them to self isolate.

Of the 8,117 who were transferred to the system, 2,710 were not reached and did not provide details of their recent contacts, illustrating the challenge faced by a program which is seen as a key tool to help loosen blanket lockdown measures.

A smartphone tracking app will be added to the program in coming weeks, although the government has not specified when.

Releasing its first data, the Department of Health’s test and trace program said it reached 31,794 contacts of the original positive cases between 28 May and 3 June, and of those it was able to reach 26,985, or 85%, and advise them to self-isolate.

Each person who tested positive and was traced had the equivalent of 5.9 contacts per person.