Figures presented to journalists in Brussels revealed that between 1 May 2004 and the end of 2010, the EU executive recruited 4,004 officials and temporary agents from the ten countries, instead of its original target of 3,508 or 16% of Commission employees.
The EU executive thus exceeded its target for recruiting staff from the new member states by 14%.
Two thirds of the new recruits were women, said Šefčovič, which means there are now more women working at the Commission than men.
Before the 2004 enlargement 46.6% of Commission staff were female, a figure that has now risen to 52.1%.
"I am delighted that the recruitment drive following the most recent enlargements has been a resounding success," said Šefčovič, vice-president for inter-institutional relations and administration.
The Commission vice-president also stressed the fact that this recruitment drive had pushed for quality and not just quantity: staff from the new member states were hired for all levels of management.
"Selecting and integrating large numbers of new staff from different countries is a challenge for any organisation. We have not only exceeded our targets, but have also found excellent, committed colleagues and have succeeded in easing them into the organisation, which in turn has given the Commission new energy," Šefčovič said.
The recruitment wave also contributed to improving the gender balance of the Commission at management level, Šefčovič announced, but despite the EU executive's efforts just 30% of its middle and senior management posts are filled by women.
The Commission vice-president said ensuring adequate geographical and gender balances were cornerstones of the EU executive's employment policy. Another consequence of enlargement is that it has slightly reduced the average age of Commission staff, he added.
Slovak national Šefčovič was quick to underline that just 20 years ago, the majority of the EU's new member states were behind the Iron Curtain and, for this reason, held the European Union's democratic traditions very close to their hearts.
Nationality quotas for the EU's most recent newcomers, Bulgaria and Romania, will remain in place until the end of this year. Šefčovič said the Commission was also on track to achieve those targets.
By pursuing a policy of trying to fulfil employment targets for EU-10 countries, the Commission acknowledged that recruitment from the ‘old' EU-15 member states had by necessity slowed down, but insisted that this would not lead to any "major geographical imbalances"as it had continued at a reasonable pace over the period in question.
Pressed further on this issue, Šefčovič admitted that it was far more difficult to attract candidates from certain old member states, like the UK and Sweden, than from the bloc's newer members, where competition for skilled graduates is lower.
Asked whether it would help to grade salaries according to nationality, the Commission vice-president suggested that instead of talking about differentiated salaries, it would be better to raise awareness of EU careers on British university campuses. Such measures, he said, were already being taken.