This is a bond ETF that tracks the Bloomberg US MBS Float Adjusted Index, which is made up of US government agency-backed mortgage-backed securities (MBS). It holds a broad range of pass-through securities issued by Ginnie Mae, Fannie Mae and Freddie Mac, weighted by market value.

As a core bond holding, it seeks stable interest income and diversification, making it suitable for investors who prefer government agency credit quality.

It is a passive (index-tracking) ETF managed by Vanguard.

The fund tracks the agency mortgage-backed securities included in the index using a sampling approach, following the performance of the broader market. Because it consists of pass-through securities issued and guaranteed by government agencies, individual issuer risk is low, and it offers a bond portfolio with diversified maturities and interest rate structures.

• Concentration in government agency-backed mortgage bonds
• Expense ratio lower than the category average

Assets under management (AUM) stand at $16.1B, and the expense ratio is 0.03% per year.

Its fee burden is lighter than that of similar passive mortgage bond ETFs such as MBB and SPMB.

Agency mortgage bond prices move with the direction of interest rates and the trend in mortgage prepayments, and during periods of rate volatility they tend to show fluctuations due to duration effects. Recent performance has also moved in step with the interest rate environment.

Fund flows follow demand for core bond assets and the interest rate cycle. In a rate-cutting phase, the price appeal of bonds stands out, while in a rising-rate period, flows tend to slow because of duration risk.

Its strengths are a low expense ratio and government agency credit quality, while interest rate sensitivity and prepayment risk are the main drawbacks.

MBB and SPMB, shown in the table, are low-cost passive alternatives that track the same agency mortgage bonds, while JMBS is actively managed and carries a somewhat higher fee. To broaden diversification beyond mortgage bonds to the US bond market as a whole, you can also consider the aggregate bond ETFs BND and AGG, and for a focus on US Treasuries, GOVT is another alternative.

Here are the points to review before investing in VMBS. Although it is a stable bond asset, interest rates, prepayments and exchange rates should be checked in advance. It is also worth considering how to allocate your core bond weighting.

Interest rate changes and mortgage prepayments are the main variables for price and returns. When rates rise, valuation losses can occur because of duration, and when rates fall, prepayments can reduce expected returns.

It is a core bond candidate suited to investors who want to diversify into government agency mortgage bonds at low cost. To broaden diversification across the bond market, BND and AGG are alternatives, and for a concentrated focus on mortgage bonds, VMBS is a suitable choice.