Strategy. Vanguard Variable Insurance Funds Equity Index Portfolio (the Portfolio) employs an indexing investment approach designed to track the performance of the Standard & Poors 500 Index (the Index), a widely recognized benchmark of U.S. stock market performance that is dominated by the stocks of large U.S. companies. The Portfolio attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the Index, holding each stock in approximately the same proportion as its weighting in the Index. The Portfolio may become nondiversified, as defined under the Investment Company Act of 1940, solely as a result of an index rebalance or market movement. Vanguard Variable Insurance Funds Equity Index Portfolio (the Portfolio) employs an indexing investment approach designed to track the performance of the Standard & Poors 500 Index (the Index), a widely recognized benchmark of U.S. stock market performance that is dominated by the stocks of large U.S. companies. The Portfolio attempts to replicate the target index by investing all, or substantially all, of its assets in the stocks that make up the Index, holding each stock in approximately the same proportion as its weighting in the Index. The Portfolio may become nondiversified, as defined under the Investment Company Act of 1940, solely as a result of an index rebalance or market movement. Show less