Vanguard Mortgage-Backed Securities Index Fund Admiral Shares 

This low-cost index fund invests in U.S. mortgage-backed pass-through securities issued by the Government National Mortgage Association (GNMA), the Federal National Mortgage Association (FNMA), and the Federal Home Loan Mortgage Corporation (FHLMC). In addition to other bond market risks, the fund is subject to prepayment risk. When mortgage refinance activity is high, the yield on the fund is likely to decrease. Investors with a medium-term time horizon and a goal of monthly income may wish to consider this fund for the fixed income portion of their portfolio.