There are a couple limitations to bond portfolio immunization.
Let's start by analyzing cash-flow matching which is a dedication strategy that is the alternative to immunization. Cash-flow matching can completely eliminate interest rate risk. The cash-flow match is setup such that the liabilities (outflows) are precisely offset by portfolio inflows on the same dates.
The challenge is that it is not easy to find bonds with the precise cash-flow payoff patterns. Moreover, bonds are subject to credit risk and potentially contingent claims risk (i.e. callable bonds) so the immunization is not risk-free presenting some limitations. Cash-flow matching will protect against any change in the shape of the yield curve including large interest rate changes (since the key rate durations of the liabilities precisely match the key rate durations of the assets).
Also, cashflow matching is more expensive than alternatives such as contingent immunization or optimizing a portfolio that minimizes a measure such as IRS (interest rate sensitivitiy). For example, if I have a view that rates are rising I would not want to use a zero-coupon bond to cash-flow match a single liability -- I'd rather receive some coupons that I can re-invest at a higher rate.
Contingent immunization can provide some scope for active management which can potentially lower the cost of immunizing a portfolio.
There are multiple immunization strategies -- single period immunization, multiple liability immunization, and immunization for general cash flows.
The necessary conditions for a successful immunization are that i) the PV of the Assets = the PV of the Liabilities, ii) the portfolio duration = duration of the Liabilities, and iii) the distribution of the durations of the assets must have higher variance than the distribution of liabilities.
As a result, some of the limitations of immunization are that:
- works for parallel shifts only (so you are exposed to yield curve risk. (Use of optimization with the Interest Rate Sensitivity measure can address this)
- Needs continuous monitoring and re-balancing of portfolio duration levels
- This re-balancing creates transaction costs
- If any bond defaults a major rebalancing or cash infusion is required
One can use derivatives (such as binary options or credit spread options) to construct portfolios that payoff if the interest rate changes by +/- 4%.