Over 70s
Mr Whitty said: "This is a quite large group, of people who are over 70 (and possibly quite healthy)".
He added: "We know that older people are at greater risk but that doesn't necessarily mean that they will get it worse."
People who have a significant health condition
Mr Whitty said: "These are mainly adults we want them to take even great care. This is critical."
He said the geoup included: "People in adult life who would normally be advised to have the flu jab with chronic conditions like chronic heart disease or chronic kidney disease."
Pregnant women
Mr Whitty described this as "a precautionary measure" because "we are early in out understanding of this virus and we want to be sure, [so will include] women who are pregnant".
Thanks for that, much appreciated.