Vaikona, absent since 9 May with a groin injury, took just four minutes to open his account, crashing over in the right corner after collecting Henry Paul's pass.
The Tongan then sprinted 35 metres to score after a mesmerising run by Paul had carved the defence apart.
His two tries helped the Bulls towards their fifth straight win as they increased their lead over Leeds.
Halifax - watched by a crowd of 9,342, a record home Super League attendance for the club - made life difficult for Bradford but the Bulls did more than enough to complete the double over the Blue Sox.
Sheffield completed a Super League double over Wakefield in an incident- packed match at Belle Vue. As the Eagles won 24-6, six players were sent to the sin-bin, another was sent off and three incidents were placed on report by referee Steve Ganson.
Heated verbal and physical exchanges between players, fans and stewards continued after the game resulting in police involvement to calm the situation.
Bright Sodje scored twice as the Sheffield Eagles went above their hosts and all but end their relegation fears.
Wakefield's Glen Tomlinson was the sixth player to be shown the yellow card for dissent and, when he continued, Ganson changed the card from yellow to red.
Warrington maintained their top-five challenge after they completed a double over the London Broncos at Wilderspool. A Simon Gillies hat-trick put them on their way to a 28-14 victory.Reuse content