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Pfizer to test a third dose of coronavirus vaccine in young children after two-dose regimen falls short

Results from the modified trials in children as young as 6 months old are expected in the first half of 2022

Pfizer and BioNTech announced Friday that their pediatric vaccine trials would be modified to include a booster dose. (David Paul Morris/Bloomberg)

Parents will have to wait for a coronavirus vaccine for their young children after Pfizer and BioNTech announced Friday that they are modifying their clinical trial to include a third shot at least two months after the initial two-dose regimen for children under age 5.

The companies reported that two doses of the pediatric vaccine failed in 2-, 3- and 4-year-olds to trigger an immune response comparable to what was generated in teens and older adults. The vaccine did generate an adequate immune response in children 6 months to 2 years old.

If three doses are successful at triggering a protective immune response, the companies expect to submit the data to regulators in the first half of next year.

“It is important to note that this adjustment is not anticipated to meaningfully change our expectations that we would file for emergency use authorization and conditional approvals in the second quarter of 2022,” said Kathrin Jansen, head of vaccine research and development for Pfizer in a call with investors.

Coronavirus vaccines have been authorized for everyone age 5 and older.

The companies have been testing two shots of a 3-microgram dose in children under 5, a small fraction of the adult dose. Because children’s immune systems are different from adults', smaller doses are expected to trigger equivalent immune protection. The trials were designed to test the safety and efficacy of the lower dose.

When the pandemic led to a lack of child care, single mothers like Denise Tyree were left in the lurch, unable to work. (Video: Hadley Green/The Washington Post)

Many parents and pediatricians hoped that if the results had been positive, Pfizer would be in a position to file for regulatory authorization early next year.

Kawsar Talaat, one of the principal investigators of the Pfizer pediatric trial and a physician at Johns Hopkins Bloomberg School of Public Health, said that while the news may be disappointing, a third dose is expected to work well to provide protection, particularly against omicron.

“I think that a third dose will give a nice boost, and honestly, this is really exciting — as we know from the adult data, three doses is probably better for omicron. And I think it’ll be good to have similar data for children,” Talaat said.

The companies are also testing a third dose in 5- to 11-year-olds and a third low-dose shot for adolescents between 12 and 17.

The decision was informed by comparing the immune response in the youngest children to older teens and young adults, and by emerging data that three doses are most protective against variants such as omicron.

This is a developing story. It will be updated.

Coronavirus: What you need to know

Vaccines: The CDC recommends that everyone age 5 and older get an updated covid booster shot designed to target both the original virus and the omicron variant. Here’s some guidance on when you should get the omicron booster and how vaccine efficacy could be affected by your prior infections.

Variants: Instead of a single new Greek letter variant, a group of immune-evading omicron spinoffs are popping up all over the world. Any dominant variant will likely knock out monoclonal antibodies, targeted drugs that can be used as a treatment or to protect immunocompromised people.

Tripledemic: Hospitals are overwhelmed by a combination of respiratory illnesses, staffing shortages and nursing home closures. And experts believe the problem will deteriorate further in coming months. Here’s how to tell the difference between RSV, the flu and covid-19.

Guidance: CDC guidelines have been confusing — if you get covid, here’s how to tell when you’re no longer contagious. We’ve also created a guide to help you decide when to keep wearing face coverings.

Where do things stand? See the latest coronavirus numbers in the U.S. and across the world. In the U.S., pandemic trends have shifted and now White people are more likely to die from covid than Black people. Nearly nine out of 10 covid deaths are people over the age 65.

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