Shares of Amazon.com Inc. AMZN, -4.60% slumped 3.8% toward a 3 1/2-month low in afternoon trading Friday, after BofA Securities analyst Justin Post said he believes sales from the ecommerce giant’s recent Prime Early Access event were less than the Prime Day event in July. The stock extended the 0.3% decline on Thursday, which came despite the S&P 500’s SPX, -2.07% 2.6% surge on the same day. Amazon had said Thursday that “tens of millions” of Amazon Prime members ordered more than 100 million items from Amazon’s selling partners. BofA’s Post said while Amazon disclosed less about its latest sales event than Prime Day, “we think sales were likely down from July.” Still, Post reiterated his buy rating and $157 stock price target, which implies about 45% upside from current levels. “Ultimately, we view this Early Access event as incrementally beneficial, as both a branding event for Prime and potentially smoothing holiday demand aiding with logistics,” Post wrote in a note to clients. The stock, which is on track for the lowest close since June 30, has tumbled 35.0% year to date while the S&P 500 SPX, -2.07% has dropped 24.4%.