Shares of Pfizer Inc. /zigman2/quotes/202877789/composite PFE -0.52% gained 1.0% in premarket trading on Friday after it announced that it will help manufacture Gilead Sciences Inc.'s /zigman2/quotes/210293917/composite GILD +0.02% COVID-19 treatment remdesivir as part of a multi-year agreement. Gilead's stock was up 0.6% on Friday before the market opened. This is a rare manufacturing deal between two of the world's largest drugmakers; "Together, we are more powerful than alone," Pfizer CEO Albert Bourla said in a news release. Remdesivir, which has received an emergency authorization from the Food and Drug Administration as a treatment for severely ill COVID-19 patients, has not been formally approved by the regulator. Since the start of the year, Pfizer's stock is down 2.3%, shares of Gilead have gained 5.9%, and the S&P 500 /zigman2/quotes/210599714/realtime SPX -1.12% has rallied 3.6%.