CCTV film has been released of a nurse who went missing after being infected with malaria during a medical trial.
Matthew Lloyd, 35, who works at Southampton General Hospital, needs life-saving treatment after taking part in anti-malarial vaccine tests.
He failed to attend a follow-up appointment in Oxford on 7 October. The CCTV film shows him in London's Kings Cross area two days earlier.
Police said it was the last confirmed sighting they had of Mr Lloyd.
Officers say he travelled to Milton Keynes and London, and possibly to Birmingham, between 1 and 7 October.
Mr Lloyd was exposed to the malaria during an appointment in London on 1 October.
'Out of character'
A police spokesman said: "There have been a number of calls from the public and possible sightings following the national media attention to Matthew's disappearance however none are confirmed at this time."
His family have said his disappearance is out of character and it is not known why he has gone missing.
On Tuesday Mr Lloyd's mother, Doreen Holland, from Somerset, urged her son to seek medical attention if he became unwell, adding "we love you son".
As well as having connections with Oxford for the clinical trial, Mr Lloyd is known to have links with Cornwall and the Avon and Somerset area.