Shares of Pfizer Inc. /zigman2/quotes/202877789/composite PFE -0.63% gained 2.5% in trading on Wednesday after Canadian regulators said they authorized using the company's COVID-19 vaccine for children between the ages of 12 and 15 years old. Pfizer developed the vaccine in partnership with BioNTech SE /zigman2/quotes/214419716/composite BNTX +0.69% . Health Canada said in a news release that this is the first coronavirus vaccine that has been authorized for this age group. The vaccine is also expected to receive emergency-use authorization for the same age group in the U.S. sometime in the next week. Pfizer's stock has gained 8.3% since these start of the year, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.08% is up 11.6%. Health Canada received an application to expand the indication of Pfizer-BioNTech's COVID-19 vaccine on April 16, 2021. The vaccine was initially authorized for use in people 16 years of age and older on December 9, 2020.