Prime Minister Boris Johnson said people over 60 and those who are clinically vulnerable are being told to be especially careful to follow the rules and minimise their contact with others during the second national lockdown.
Anyone who was formally notified that they should shield last time and not go out to work will be advised not to go out to work this time.
However, formal shielding as happened during the March and April lockdown - where people were told not to leave home for any reason - will not be brought in.
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Professor Whitty said it was right that vulnerable people who were shielding during the previous lockdown continued to take extra precautions this time around, adding: "We learnt a lot from last time with the shielding programme - some of the things worked but some of the things did not.
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"There were both some practical problems, and there was also the issue of people having significant problems with loneliness and feeling completely cut off from society.
"What we're trying to do is avoid those downsides to shielding, whilst reinforcing the message that for people who are particularly vulnerable they do need to take even greater precautions than the general public."
Mr Johnson added: "I know how tough shielding was and we will not ask people to shield again in the same way.
"But we are asking those who are clinically extremely vulnerable to minimise their contact with others and not to go to work if they are able to work from home."
