While nirmatrelvir/ritonavir (Paxlovid) is currently available for treatment of COVID in children aged 12 years or older, a new study could expand its use to a younger population.

Robust reductions in SARS-CoV-2 RNA concentrations from baseline through the end of treatment were shown, and no COVID-related hospitalizations or deaths were reported among children younger than 12 years who received the drug.

“Results of this study provide important pharmacokinetics, safety, and supportive efficacy data to prescribers for clinical decision-making when treating pediatric patients aged at least 6 years with mild-to-moderate COVID-19 who are at risk of progression to severe disease,” wrote the researchers, who are current and former employees of Pfizer, the manufacturer of Paxlovid.

The COVID hospitalization rate was 63.6 per 100,000 from 2024 to 2025 in those younger than 4 years and 8.9 per 100,000 in those aged 15-17 years. During the first 3 years of the pandemic, provisional data attributed 776 deaths among children younger than 4 years to COVID, while 1071 deaths were recorded among teens aged 15-18 years.

The FDA granted emergency use authorization (EUA) for Paxlovid for high-risk children aged 12 years or older who weigh at least 40 kg (88 lb) in December 2021. The current results are from an ongoing clinical trial, part of a post-marketing commitment from the manufacturer.

The study, published in Pediatrics, provides new information about dosage for younger and smaller children than current authorization for older children, said Mari Nakamura, MD, MPH, medical director of Antimicrobial Stewardship at Boston Children’s Hospital in Boston.

“Having a study that provides more data that could lead to expansion of the EUA, or maybe eventually pediatric approval, is helpful,” she said.

Study Details

Researchers analyzed data from 75 children aged 6-17 years as part of interim results of the ongoing phase 2/3 interventional, open-label study.

Participants had confirmed SARS-CoV-2 no more than 72 hours before enrollment, were not hospitalized, and were symptomatic within 5 days prior to enrollment. They had at least one underlying medical condition, such as chronic lung disease or diabetes, associated with high risk for progression to severe COVID.

Participants weighing at least 40 kg received 300 mg of nirmatrelvir/100 mg of ritonavir, while those weighing between 20 kg and 40 kg received 150/100 mg, both twice a day for up to 5 weeks.

Efficacy was extrapolated by matching drug exposure in children to that in adults with COVID. Simulated exposure for both cohorts indicated more than 90% of participants achieved minimum nirmatrelvir concentrations above the 90% effective concentration after the first dose.

Reported adverse outcomes included diarrhea and headache (4%). No participants discontinued the study because of a treatment-related adverse event.

The Pediatric Infectious Diseases Society recommends nirmatrelvir/ritonavir for pediatric patients who do not require hospitalization.

The Infectious Diseases Society of America is currently developing a COVID guideline that will include pediatric recommendations, Nakamura said.

A spokesperson for Pfizer declined to say whether the company would seek full approval of Paxlovid in children older than 6 years. The FDA granted approval for the drug in the treatment of COVID in adults in May 2023.

Nakamura noted that remdesivir is the only alternative COVID treatment for children younger than 12 years or weighing < 40 kg. It requires going to an infusion center for 3 consecutive days for daily infusions. Remdesivir is approved for pediatric patients weighing at least 1.5 kg.

Pfizer funded the study. Nakamura reported having no financial conflicts of interest.

Brenda Sandburg is a freelance journalist for Medscape Medical News. She has written about the biopharmaceutical industry and legal issues for the Pink Sheet and American Lawyer Media.