Immunization (finance)

In finance, interest rate immunization is a portfolio management strategy designed to take advantage of the offsetting effects of interest rate risk and reinvestment risk. In theory, immunization can be used to ensure that the value of a portfolio of assets (typically bonds or other fixed income securities) will increase or decrease by the same amount as a designated set of liabilities, thus leaving the equity component of capital unchanged, regardless of changes in the interest rate. It has found applications in financial management of pension funds, insurance companies, banks and savings and loan associations. Immunization can be accomplished by several methods, including cash flow matching, duration matching, and volatility and convexity matching. It can also be accomplished by trading in bond forwards, futures, or options. Other types of financial risks, such as foreign exchange risk or stock market risk, can be immunised using similar strategies. If the immunization is incomplete, these strategies are usually called hedging. If the immunization is complete, these strategies are usually called arbitrage. Immunisation was discovered independently by several researchers in the early 1940s and 1950s. This work was largely ignored before being re-introduced in the early 1970s, whereafter it gained popularity. See Dedicated Portfolio Theory#History for details. Frank Redington is generally considered to be the originator of the immunization strategy. Redington was an actuary from the United Kingdom. In 1952 he published his "Review of the Principle of Life-Office Valuations," in which he defined immunization as "the investment of the assets in such a way that the existing business is immune to a general change in the rate of interest." Redington believed that if a company (for example, a life insurance company) structured its investment portfolio assets to be of the same duration as its liabilities, and market interest rates decreased during the planning horizon, the lower yield earned on reinvested cash flows would be offset by the increased value of portfolio assets remaining at the end of the planning period.