Saracens prop Vunipola, 21, has been called up to the 32-man squad as an injury replacement for Alex Corbisiero while Youngs, who was taken on the summer tour to South Africa, comes in for Rob Webber.
Further additions see wing Ugo Monye, who has impressed for Harlequins so far this season, and James Haskell, who is back at Wasps following spells in France, Japan and New Zealand, included in place of the injured Ben Foden and Tom Croft respectively.
England head coach Stuart Lancaster said: “As a coaching team we can’t wait to go into camp and get the guys focused on what will be a massive challenge in the QBE Internationals – Fiji and then the three major Southern Hemisphere teams in successive weeks.
“We have been impressed with some of the rugby we have seen in the Aviva Premiership and Heineken Cup and are looking forward to the players bringing that form to Twickenham.
“It’s great to be able to give Mako a chance in the squad. He has come through our age grade sides and made a real impact at Saracens. Likewise Tom Youngs, who was with us on tour in South Africa, and we know what James Haskell and Ugo Monye are capable of if they get their opportunity.”
Meanwhile, the England Saxons coaching team has been finalised, with John Fletcher joining as backs coach for the internationals against the Ireland Wolfhounds and Scotland A in the New Year.
The former Newcastle Falcons boss returns to Kingston Park on 1 February for the match against the Scots, a week after the Saxons face the Wolfhounds in Ireland.
Mouritz Botha (Saracens)
Dan Cole (Leicester Tigers)
James Haskell (London Wasps)
Phil Dowson (Northampton Saints)
Dylan Hartley (Northampton Saints)
Tom Johnson (Exeter Chiefs)
Courtney Lawes (Northampton Saints)
Joe Marler (Harlequins)
Ben Morgan (Gloucester Rugby)
Tom Palmer (London Wasps)
Geoff Parling (Leicester Tigers)
Chris Robshaw (Harlequins)
Mako Vunipola (Saracens)
Thomas Waldrom (Leicester Tigers)
David Wilson (Bath Rugby)
Tom Wood (Northampton Saints)
Tom Youngs (Leicester Tigers)
Anthony Allen (Leicester Tigers)
Chris Ashton (Saracens)
Brad Barritt (Saracens)
Mike Brown (Harlequins)
Danny Care (Harlequins)
Lee Dickson (Northampton Saints)
Owen Farrell (Saracens)
Toby Flood (Leicester Tigers)
Alex Goode (Saracens)
Jonathan Joseph (London Irish)
Ugo Monye (Harlequins)
Charlie Sharples (Gloucester Rugby)
Manu Tuilagi (Leicester Tigers)
Jordan Turner-Hall (Harlequins)
Ben Youngs (Leicester Tigers)
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BIOGRAPHY: Marcus Rashford