Pfizer said on Wednesday it has begun a mid-to-late-stage study of its antiviral COVID-19 pill for non-hospitalized children aged 6-17 years who are at high risk of developing severe illness.

Pfizer’s Paxlovid pill is authorized for emergency use in the United States for kids 12 years or older and high-risk adults. But there are no oral antiviral treatments for COVID-19 authorized in the United States for younger children.

The drugmaker plans to enroll 140 children in the study across two groups of 6- to 17-year-olds, with one group including those at least 40 kilograms in weight and the other weighing between 20 kgs and 40 kgs.

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“Since the beginning of the pandemic, more than 11 million children under the age of 18 in the United States alone have tested positive for COVID-19, representing nearly 18% of reported cases and leading to more than 100,000 hospital admissions,” said Pfizer Chief Scientific Officer Mikael Dolsten.

Pfizer said on Wednesday it was also working to develop an age-adjusted formulation of the drug for patients younger than 6 years and will start enrolling three groups of kids under 6 once the modified formulation becomes available.

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Data from a mid-to-late stage study in November showed Paxlovid was nearly 90% effective in preventing hospitalizations and deaths compared to placebo, in adults at high risk of severe illness.