Contact tracing

England's chief medical officer Chris Whitty says social distancing must "continue for a long period of time".
Covid-19 arrived on a passenger plane. It took four months for the government to make changes to air travel.
Baroness Dido Harding said the alternative system, which aims to identify where a patient caught Covid-19, is being trialled in Leicester.
Lord Bethell says the NHSX app, which has been beset by delays, is no longer a "priority".
It was heralded as the best way for life to return to normal, but has ended up in near embarrassment. Insiders now reveal what went wrong.
Government testing tsar John Newton gives hope to Britons eyeing up a summer holiday.
Many questions remain unanswered about the new NHS system unveiled by Boris Johnson.
But Keir Starmer hits back as PM demands Labour leader be less "negative" about the pandemic.
Security and police officers deployed as more people set to return to work. Here's the latest.
Recruitment company tells job applicants government is considering an "alternative" app, but later says this was a "miscommunication and false".