For weeks, experts have been telling parents in the U.S. to expect a low-dose Pfizer COVID vaccine for children under age 5 to become available by the end of the year or in early 2022. But new trial results show an inadequate immune response in many of these children. This means the timeline of vaccine availability for this age group has been pushed back significantly.
On Friday, Pfizer announced that although two shots of the new low-dose vaccine appeared safe in young children, the 3μg doses do not provide adequate protection against COVID in children 2 to 5. (However, early indications suggest they were effective in children 6 months to 24 months). Pfizer is updating the trial to include a third dose for children under 5, but the extra step will set back the authorization timeline. Pfizer estimates it will be mid-2022 before infants, toddlers, and preschoolers could get the shot.
Unfortunately, this news piles on top of the start of an Omicron-driven COVID surge in the U.S. amid concerns about holiday travel. With all that in mind, Fatherly spoke to two immunology and infectious disease experts to get a candid take on the status of COVID vaccines for those under five, how the shot is expected to stack up against Omicron, and how you should proceed with holiday plans during the COVID-19 pandemic.
What Happened With the Under-5 Pfizer Vaccine Trial?
The two-dose trial “didn’t didn’t meet the antibody level required by the [Food and Drug Administration],” says Kawsar Talaat, MD, a pediatric infectious disease specialist at Johns Hopkins Bloomberg School of Public Health. Early measurements in the study suggested that kids aged 2 to 5 weren’t building adequate antibody levels in response to the vaccine. But we actually don’t know anything about the two-dose vaccine’s efficacy, or its ability to prevent COVID in young children, Talaat says.
She’s hopeful that the three doses will be very effective. But the changes to the trial “are going to delay the authorization for kids under 5 into the first half of 2022, as opposed to the first quarter,” she says.
“The company said in the first half of 2022, so that might be by June,” says Janet Englund, MD, an expert in pediatric infectious disease and virology at Seattle Children’s Hospital. But this will depend on how fast the sites can recruit children and how well the vaccine works according to blood tests and effectiveness against infection. “It involves vaccinating and getting blood samples and following up [in] several thousand children around the world,” Englund says. “That takes time to do.”
Is the Trial Delay due to a Safety Concern?
In short, no.
“There are no safety concerns. The concerns are in the antibody levels produced by the vaccine, which is what we call ‘immunogenicity,’ and that can impact the effectiveness of vaccines,” Englund says. In its press release, Pfizer said the vaccine appeared to have a favorable safety profile for young children.
The 3μg dose being tested is much lower than what’s been given to older age groups: 10μg for kids aged 5 to 11 and 30μg for everyone 12 and up. “They really dropped it down [from previous trials] to 3 micrograms, which is one tenth of the adult dose and one third of the dose for older children,” says Talaat, who is also the site Principal Investigator for the pediatric vaccine trial at John Hopkins.
Rather than up the dose – which, so far, appears to produce adequate antibody levels in toddlers 6 to 24 months old – Pfizer will begin testing a third shot for all children aged 5 and under, given at 2 months after the second dose.
“The really reassuring thing is this is the first vaccine ever to be used in hundreds of millions of adults before it ever went into adolescents, and then millions of adolescents before it was used in children,” Talaat says. There’s “never been a vaccine that’s been scrutinized more in terms of safety.”
Why Are Young Children Lagging Behind the 5 to 11 Group?
The main reason that it’s taken the under-5 vaccine trial so long to get results on efficacy of the two-dose COVID vaccine is that all vaccines and drugs are first tested in adults, then teens, then children, and finally younger children, Englund says. This is for ethical and safety reasons – if there are issues with the vaccine in older kids, researchers want to wait until they’re cleared up to test the vaccine on younger kids – and in the case of COVID, also because children don’t develop as severe disease as older adults, she says.
But another big reason why the trial is taking longer is because it’s more difficult to perform research on young kids. “For under five, they don’t really have a good sense of why they are there or what you are doing to them,” Talaat says. “You have to be slower and approach them differently.” That can include taking the time to calm them down before giving them the shot, or even playing with the kids to make them comfortable, she says.
And because it takes more time per child, and staff and space are limited, a trial in young children inherently takes longer – even without setbacks related to dosage efficacy.
What Does the Delay Mean for Omicron?
“It will be a matter of time before we have competing [Delta and Omicron] surges,” Talaat says. Many parents had hoped that an early 2022 vaccine authorization might mean some added protection for their youngest kids against the rising variant of concern. But Friday’s report takes this option off the table.
As for how the virus will target children specifically, for now “we don’t have much of an idea of the incidence of Omicron in children,” says Englund, who is a site investigator at Seattle Children’s Hospital, where she conducts Pfizer vaccine investigational studies in children. Reports from South Africa suggest the Omicron variant could be more infectious in children than previous versions of the virus, but there’s not enough data to be sure.
It’s possible that this apparent higher transmissibility in kids has more to do with vaccination rates than how the disease targets children, Englund says. Young kids are expected to make up an increasing proportion of Omicron cases, and COVID in general, she says. This is especially true in cities with high vaccination rates because young children make up a large proportion of the unvaccinated population. Unvaccinated children who haven’t been infected have no antibodies, she says. “If you look at the whole population, the people that are going to get infected with COVID – a variant or not — are more likely to be those that aren’t vaccinated.”
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