A closely watched gauge of expected stock-market volatility is at its highest level in more than two years as stocks extended a brutal selloff that has been at least partly promoted by growing fears of the economic impact of COVID-19. The Chicago Board Options Exchange Volatility Index, or VIX VIX, +11.18% was trading up at around 42 on Friday, marking its highest level since early February of 2018, according to FactSet data. The weekly slide for the index, up 144%, would represent its firmest weekly advance since the gauge was created in 1993. The VIX, often referred to as Wall Street's fear gauge, tends to rise when stocks fall. The VIX tracks options trading on the S&P 500 SPX, -2.38% to measure expectations for stock turbulence over the coming 30 days. The stress on the equity market has helped to considerably boost the VIX, with the S&P 500, the Dow Jones Industrial Average DJIA, -3.03% and the Nasdaq Composite Index COMP, -1.48% all on track for their sharpest weekly slides since the 2008 financial crisis. Worries about COVID-19, the infectious disease that reportedly originated last year in Wuhan, China, has spread rapidly throughout the world and investors are worried about the impact to global supply chains and economies.