Shares of Regeneron Pharmaceuticals Inc. /zigman2/quotes/203149337/composite REGN -0.43% gained 2.1% in premarket trading on Wednesday, the day after the company said the U.S. government had purchased an additional 1.4 million doses of its monoclonal antibody treatment for COVID-19 for $2.9 billion. The treatment, which costs $2,100 per dose, is free to Americans at high risk of hospitalization and death who have tested positive or have been exposed to the virus. Most of the doses are expected to be delivered in the final three months of 2021. "With COVID cases, hospitalizations, and deaths all elevated again in the U.S., demand is likely to remain high through year-end, and most likely through the winter," SVB Leerink analyst Geoffrey Porges told investors. He predicts that the treatment will generate $5.4 billion in total sales in 2021. Regeneron's stock has soared 33.5% so far this year, while the broader S&P 500 /zigman2/quotes/210599714/realtime SPX +0.75% is up 18.9%.