Pfizer Starts Testing Its Covid-19 Pill in Children

The first child enrolled in the study on Monday. Pfizer expects results by the end of the year, said Annaliesa Anderson, who leads the company’s Paxlovid research.

Should results from the pediatric study prove positive, the antiviral would be the first Covid-19 pill for children under 12 years and an especially important remedy for those with underlying health conditions who cannot be vaccinated or whose parents don’t want them to get shots.

“When it comes to Covid-19, they’re not exempt from the severe outcomes, and they do need treatment to prevent severe disease, particularly if they have risk factors that would lead to that,” Dr. Anderson said in an interview.

Uptake of vaccines for children under 12 years has been slower than authorities had hoped, and the FDA has delayed making a decision whether to authorize a shot for children under 5.

Most children who become infected with Covid-19 have mild or no symptoms at all, and they are much less likely than adults to be hospitalized or die.

Yet children were hospitalized in larger numbers during the recent Omicron surge than previously in the pandemic. The hospitalization rate for children under 18 years was 7.1 per 100,000 at the Omicron peak, compared with 1.8 per 100,000 at Delta’s peak in September, according to the Centers for Disease Control and Prevention.

More than 78,800 children have been admitted to the hospital with confirmed Covid-19 since June 30, nearly three-quarters of which have come since the end of September, according to the U.S. Department of Health and Human Services.

Many of the hospitalized children had underlying health conditions or were admitted for non-Covid-19 reasons, but also tested positive for the virus, according to research and the government.

Paxlovid was the first easy-to-take Covid-19 pill authorized for use in the U.S. Paxlovid consists of a drug named nirmatrelvir that Pfizer developed and an older, commonly used antiviral called ritonavir. Paxlovid is taken twice daily over five days.

In a pivotal study among people 18 years and older, it reduced the risk of hospitalization or death by 88% if taken within five days of symptoms.

In the new study, Pfizer plans to enroll about 140 children vaccinated and unvaccinated who have at least one risk factor for severe Covid-19, such as obesity, diabetes or a weak immune system.

The study will evaluate whether Paxlovid reduces the risk that the young study subjects will be admitted to a hospital or die within a month of taking the treatment. Pfizer also will collect blood samples from the children to assess how much of the virus declines over time.

Researchers plan to study the dosage currently authorized in a group of children ages 6 to 17 years who weigh at least 88 pounds.

A second group of children, who weigh between 44 and 88 pounds, will receive half the dosage of nirmatrelvir although the ritonavir dosage will remain the same.

All the children in the trial will get Paxlovid, rather than some getting a placebo, because testing has already shown use of the drug protects against Covid-19, Dr. Anderson said.

Quickly enrolling children, within five days of showing symptoms, “will be the biggest challenge, making sure we can enroll the children within the time frame,” Dr. Anderson said.

Researchers plan to eventually enroll children under 6 years, although they will take a lower-dose version that is still in development.

The U.S. has committed to purchasing 20 million courses of Paxlovid.

—Jon Kamp contributed to this article.

Write to Jared S. Hopkins at [email protected]