Shia Muslims not only pay 2.5% left over from savings as zakat, but also an additional 20% as khums or general charity. However most prefer to pay directly to the needy.
Note that it is forbidden to give Zakat and charity to the descendants of the Prophet. Thus Zakat revenues and charities go to those needy who are NOT the descendants of the Prophet, while half of the Khums goes to those needy people who are the descendants of the Prophet.
One should also note that during the history of Islam till now, the descendants of the Prophet were being prosecuted every where and were deprived of their rights. Also a minority among Muslims continue to pay Khums. In other words, only 20% of all Muslims pay Khums which heavily decreases the amount of what the needy descendants of Prophet get from Khums (=20%*1/2*1/5=2%) when it is compared with the amount that needy people who are not the descendants of the Prophet get through Zakat from all Muslims (2.5%) plus all the charities which could be much more than 2.5%.