Drugmaker Pfizer has again modified the protocol for its late-stage study of its vaccine against the new coronavirus, this time to include more young participants.

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The company said on October 12 that it's received permission from the Food and Drug Administration to include adolescents aged 12 through 15 in its global COVID-19 vaccine study. New York-based Pfizer originally planned for 30,000 participants, but in September expanded that to 44,000 people. That increase was made to boost diversity in the trial population, specifically by including 16- and 17-year-old teens, as well as stable patients with some common chronic infections: hepatitis B, hepatitis C and HIV.

Pfizer's trial also includes significant numbers of Hispanic, Black, Asian and Native American participants, plus many people aged 56 through 85. The diversity is aimed at providing information on how safe and effective the experimental vaccine is in people of different ages and backgrounds.