Pfizer-BioNTech is moving into the next stages of development for a version of its COVID-19 antiviral pill that will be safe for children younger than 12 years of age.

On Wednesday, the company announcedthat it was advancing to stage 2 and stage 3 trials for a modified version of its Paxlovid antiviral pill that will be for younger children. Paxlovid is currently one of only two antiviral pills authorized for emergency use by the federal government alongside Merck and Ridgeback’s Molnupiravir.

According to Pfizer, the trial is enrolling about 140 participants and will evaluate them in two cohorts to determine the effects of different doses based on weight. Currently, only those weighing 88 pounds or more are authorized to receive Paxlovid, so the cohort is being broken up into groups that will get different doses of the pill's two ingredients: nirmatelvir and ritonavir.

The first cohort, weighing at least 88 pounds, will receive 300 milligrams (mg) of nirmatrelvir and 100 mg of ritonavir by mouth twice a day for five days, the same amount prescribed today for use. The second cohort weighs between 44 and 88 pounds and will get a smaller dose: 150 mg of nirmatrelvir and 100 mg of ritonavir by mouth twice a day for five days.

If successful, the pill would help reduce the severity of COVID-19 cases in children. With the arrival of the Omicron variant at the end of last year, pediatric hospitalizations rose sharply. A study by the Centers for Disease Control and Prevention (CDC) reported in February that rates of infection among children eclipsedthe previous peak seen during the Omicron variant.

According to Pfizer, Paxlovid has been an effective treatment for those infected with COVID-19. It contends that its pill has a nearly 90% effectiveness rate in warding off hospitalizations in high-risk patients.

If Pfizer’s pill can become more widely available, it would also dovetail well with President Joe Biden’s recently unveiled plan to fight COVID-19. The plan includes a goal of expanding access to COVID-19 antiviral pills

One important item in the plan is one Biden previewed in his first State of the Union address last Tuesday dubbed “Test-To-Treat.” The program would ensure a patient receives testing and access to treatment for COVID-19 on the same day, all at no cost.

As part of this program, the Biden administration aims to increase the number of antiviral pills to treat COVID-19 like Paxlovid. The pill was approved by the Food and Drug Administration (FDA) last year, but manufacturing was delayedby the arrival of the Omicron variant of COVID-19 in late November.