WASHINGTON — In the past 10 months, as tens of millions of children and teens received the Pfizer-BioNTech vaccine, the company’s main rival, Moderna, sat on the sidelines, the opportunity limited to adults.
But Moderna may now be poised for a comeback at a pivotal moment in the country’s vaccination campaign. The company is expected to send federal officials first data this week on how well the coronavirus vaccine is working for the nation’s youngest children.
About 18 million children under the age of 5 are the only Americans not yet eligible for vaccination. And while adoption for older children is slow, many parents are still anxiously awaiting the opportunity to protect their babies, toddlers and preschoolers.
Moderna is going up against Pfizer-BioNTech for the chance to vaccinate this group in the hopes it has found what some scientists call the “Goldilocks” dose: strong enough to provide lasting protection, but not so strong that the widespread worrisome side effects, such as high fever.
Moderna has opted for a two-dose regimen of one-quarter the strength of the adult dose for children under 6. Pfizer is expected to seek approval next month for a three-shot regimen for children under 5 years of age, with doses one-tenth as strong as those for people 12 years and older.
Moderna is also expected to release data soon from its clinical trial on the following age group: children ages 6 to 11.
dr. Yvonne Maldonado, a Stanford professor of pediatric infectious diseases and a principal investigator at the Stanford site of Pfizer’s pediatric vaccine trials, said new data from both Moderna and BioNTech in the coming weeks will provide critical insight into the effectiveness of their pediatric injections. She said researchers are closely monitoring whether Moderna’s stronger doses “result in more robust immune responses” than Pfizer’s injections induced in young children.
A series of new studies that raise questions about how long Pfizer’s lower doses protect primary school-age children have sparked the interest of federal scientists and vaccine experts in Moderna’s choices.
dr. Ofer Levy, a pediatric expert at Harvard Medical School and a member of the Food and Drug Administration’s independent advisory committee on vaccines, said he thought Pfizer may have selected too low a dose for 5- to 11-year-olds “in the understandable sense.” priority to maximize safety.”
To date, Pfizer has been the only player in vaccinating younger Americans, winning authorization to vaccinate 12- to 15-year-olds last May, followed by 5- to 11-year-olds in October. The adult permit also applies to 16 and 17 year olds.
Moderna applied for permission to vaccinate teens last June, but the FDA delayed considering the request due to concerns about the risk of myocarditis, an inflammation of the heart associated with both the Moderna and Pfizer injections.
More than 22 million people in the United States under the age of 18 are now fully vaccinated with the Pfizer vaccine, but uptake is declining. For example, only about one in four children ages 5 to 11 have been fully vaccinated, while that group has been offered injections for more than four months.
But there is still a demand to protect the youngest children as more of the country is exposed, more parents return to work and the summer travel season approaches.
Compared to adults, “there is no doubt that in children the benefit of an effective vaccine is less, because fewer actually get sick,” said Dr. Eric Rubin, an infectious disease expert at the Harvard TH Chan School of Public Health and a member of a Food and Drug Administration advisory panel.
“But it will benefit some individuals,” he said. “It will save some lives.” According to the Centers for Disease Control and Prevention, 336 children under the age of 5 have died of Covid since the start of the pandemic in the United States.
Hopes that the youngest children would be covered soon rose last month after regulators pressured Pfizer-BioNTech to submit preliminary results of the three-dose trial. The FDA wanted to start the vaccination campaign with two doses pending the final results of three.
But that effort faltered when new data from Pfizer covering more of the Omicron peak convincingly showed that two doses provided insufficient protection against symptomatic infection.
More detailed results of the Pfizer and Moderna trials are now appearing at about the same time. And while neither company knows yet whether their vaccines will be effective enough for the youngest age group, both say their research shows they are safe.
“We haven’t seen anything untoward at this time, so we are confident in the safety profile,” said Dr. Paul Burton, Moderna’s Chief Medical Officer, in an interview.
Amy Rose, Pfizer’s spokeswoman, has said that after careful research, Pfizer-BioNTech has selected the “safest and most acceptable dose” for young children. The companies have said they are hopeful that a three-shot regimen will provide strong protection for children under the age of 5. Pfizer is testing a 10-microgram dose for 5- to 11-year-olds, a third of the adult and teen dose; and 3 micrograms for children under 5 years of age.
Moderna suggests a significantly higher dosage than Pfizer in all three pediatric age groups: 100 micrograms, the full adult dose, for children 12 to 17 years of age; 50 micrograms in children 6 to 11 years of age and 25 micrograms in children under 6 years of age. Regulators are expected to review the company’s data for all three age groups simultaneously.
“We’re really behind those doses,” said Dr. Burton. While federal officials say both Pfizer and Moderna vaccines decline in strength over time, some studies in adults have suggested that Moderna’s protection lasts longer. “I think it’s the dose,” said Dr. Burton.
He said early results showed that a 50 microgram dose of Moderna induced a “robust immune response” in children ages 6 to 11. While the total number of infections was small, researchers hope the trial will help reveal how well the vaccine prevents disease, not just how high it raises antibody levels.
dr. Philip Krause, who recently retired as a senior vaccine regulator at the FDA, said the agency spent a lot of time last year raising concerns about the safety of Moderna’s vaccine for people under the age of 18, with some studies suggesting a higher risk. for myocarditis by the company’s injection. than Pfizer’s.
“The question is always, what is the dose that triggers an immune response that we think is likely protective?” he said. “You couldn’t really test to find out the rate of myocarditis because it’s rare, but you could ask, ‘What are we sacrificing in the immune response by lowering the dose, and do we think that’s important?'”
Partly because of concerns about myocarditis, the CDC recently encouraged some people ages 12 or older, especially boys and men ages 12 to 39, to wait eight weeks between their first and second Pfizer or Moderna injections. Studies have shown that teenage boys and young men are most at risk of developing the side effect.
dr. Burton said the research had been generally reassuring, including recent UK data showing that myocarditis was very rare and usually mild in both Pfizer and Moderna recipients.
But dr. Walid F. Gellad, a drug safety expert at the University of Pittsburgh, said it remained unclear whether the higher dosage of Moderna could increase the risk of myocarditis in young children. The company’s pediatric studies are likely far too small to determine the risk of the side effect, he and other experts said.
Moderna’s new push also comes after several studies raised questions about the protection that two doses of Pfizer-BioNTech’s vaccine provide for children ages 5 to 11. Researchers at the New York State Department of Health recently found that protecting against infection by two doses faded considerably within a few weeks.
CDC researchers separately found that during the Omicron wave, the effectiveness of two doses of the Pfizer Injection against moderate forms of the disease in children ages 5 to 11 decreased significantly.
The studies have sparked a debate among vaccine experts as to whether a stronger dose would have been better or whether those children need third doses. Booster shots are now allowed for anyone 12 and older. Pfizer expects results next month from its study of a three-dose regimen for the younger children.
dr. Gellad said it was possible that the dose of Pfizer for 5- to 11-year-olds was too low, but scientists couldn’t be sure yet. He said he expected regulators to be particularly careful when considering higher doses for young children, given the relatively low risk of them now contracting Covid and becoming seriously ill.
Amid all the questions, one thing is clear: Going back and forth over which vaccine will be better for young children could discourage its uptake.
Alison M. Buttenheim, a behaviorist at the University of Pennsylvania, said those who considered vaccination found comfort in certainty. Otherwise, “that will just clear the way for you to say, ‘I’m going to wait,'” she said. “A lot of people are uncomfortable with the evolving science.”