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There are special dosing considerations for kids who turn 12 years old in the middle of their COVID-19 primary vaccination series.(Source:Alamy)

Children who turn 12 years old in the middle of the two-dose primary series of Pfizer Inc./BioNTech SE’s COVID-19 vaccine got special attention at a Centers for Disease Control and Prevention advisory committee meeting on use of the vaccine’s lower-dose pediatric formulation in children ages 5-11 years old.

At a 2 November meeting, members and liaison representatives of the Advisory Committee on Immunization Practices questioned what dosage strength should be given to an 11 year-old who turns 12 after getting the first dose of the mRNA vaccine but prior to receipt of the second dose.

Some panelists also questioned whether older 11 year-olds, including those who are obese, should wait until their 12th birthday to be vaccinated with the higher dose authorized for those ages ≥12 years.

The answer, in short, is the dose should be based on the child’s age on the day of vaccination, the CDC said. However, the FDA is allowing for some flexibility in dosing for kids on the cusp of age 12.

Caught In The Middle Of A Dosing Increase

The FDA has authorized a 30 mcg mRNA dose of the Pfizer/BioNTech vaccine for use in individuals ages ≥12 years, with two doses given three weeks apart as the primary series. Although the emergency use authorization for the pediatric age group ages 5-11 years follows a similar dosing schedule, the authorized dose is only 10 mcg mRNA, one-third that used for the 12-and-older population. (With Pfizer EUA For 511 And Moderna Delay For Adolescents US FDA Walks Myocarditis Tightrope)

The difference in doses, and the three-week interval between doses, means some children could shift into the older age bracket before they get their second dose.

ACIP member Pablo Sanchez, a professor of pediatrics at Nationwide Children’s Hospital, asked whether any subjects in Pfizer’s Phase II/III immunogenicity and safety study of more than 4,600 children ages 5-11 years turned 12 prior to the second dose and, if so, what dosage amount they received.

“We did have children who turned 12,” said Alejandra Gurtman, Pfizer’s VP of vaccine clinical R&D. “I believe that we had about seven children. All of them of received a second dose of 10 mcg. So the study was designed knowing that this could happen and with the intention that the second dose would be the same as the first.”

In its authorization of the pediatric formulation, the FDA made special allowance for dosing of 11 year-olds on the cusp of turning 12. The agency addressed the issue through a footnote in the health care provider EUA fact sheet for the 5-11 age group. (See box.)

Pfizer/BioNTech Health Care Provider Fact Sheet

  • “Notwithstanding the age limitations for use of the different formulations and presentations described above, individuals who will turn from 11 years to 12 years of age between their first and second dose in the primary regimen may receive, for either dose, either: (1) the Pfizer-BioNTech COVID-19 Vaccine formulation authorized for use in individuals 5 through 11 years of age (each 0.2 mL dose containing 10 mcg modRNA) (orange cap); or (2) COMIRNATY or one of the Pfizer-BioNTech COVID-19 Vaccine formulations authorized for use in individuals 12 years of age and older (each 0.3 mL dose containing 30 mcg modRNA) (gray and purple cap).”


At the ACIP meeting, Doran Fink, deputy director for clinical in the FDA’s Division of Vaccines and Related Products Application, explained the FDA’s approach to dosing in this age group.

“What FDA has authorized is that either the 10 mcg formulation that is authorized for use in ages 5-11 or the 30 mcg formulation that is authorized for use in ages 12 and above can be used for either dose one or dose two in the situation where a child will be 11 years old when they are set to receive dose one and then turns 12 before they are set to receive dose two,” Fink said.

“Of course, the most data-driven approach, the approach for which the data are actually available, would be for a 10 mcg dose be given to a child who is 11 at the time the dose is administered, and for a 30 mcg dose to be given to a child who is 12 at the time that dose is administered,” Fink said.

“However, FDA did recognize that there may be some situations in which there would be a need for flexibility and the totality of data do support this more flexible approach where there would be a change in age occurring in between the two doses,” he said. “It’s up to CDC and ACIP to make whatever they consider to be the most appropriate recommendations for implementation of the doses such as they’re authorized.”

The increased risk of myocarditis reported after the second dose of mRNA vaccines, particularly in older male adolescents and younger men, could give providers pause in giving a newly turned 12 year-old a 30 mcg dose after an initial 10 mcg dose. (Pfizer Vaccines Benefit-Risk Assessment In Older Male Adolescents A Close Call Due To Myocarditis)

Clinical Considerations

In a presentation on interim clinical considerations for use of the Pfizer/BioNTech vaccine in children ages 5-11 years, the CDC’s Kate Russell Woodworth said that unlike many medicines, vaccine dosages are based on age, not size or weight. Consequently, children should receive the age-appropriate vaccine formulation regardless of their size and weight.

In addition, the dosage should be based on the child’s age on the day of vaccination, Woodworth said.

However, if a child turns 12 in between their first and second dose and receives the 10 mcg for their second dose, they do not need to repeat the dose and this is not considered an error under the EUA, Woodworth said.

Nevertheless, she emphasized that the 10 mcg and 30 mcg formulations of the Pfizer/BioNTech vaccine are not interchangeable, and administration errors may occur if children are inadvertently given the wrong dose.

For example, if a child age 5-11 years inadvertently receives 30 mcg dose for their first dose, they should receive a 10 mcg dose 21 days later and be considered as having completed the primary series. If a child age 5-11 years inadvertently receives a 30 mcg dose for their second dose, they also should be considered as having a completed primary series. In both scenarios,  such administration errors should be reported to the CDC.

Although ACIP members questioned what dose should be given to those who are newly 12 or on the cusp of turning 12, there was little discussion or debate by the panel on the issue.

The committee voted 14-0 to broadly recommend use of the Pfizer/BioNTech vaccine in children ages 5-11 years without regard to the presence or absence of underlying medical conditions, history of symptomatic or asymptomatic SARS-CoV-2 infection, or seropositivity. (See sidebar for story.)

CDC director Rochelle Walensky endorsed the ACIP recommendations within hours of the meeting’s conclusion.

No Extra Dose For Immunocompromised Kids

For the 12-and-older population, an additional dose of Pfizer/BioNTech vaccine is authorized for those individuals who have undergone solid organ transplantation or are diagnosed with conditions considered to have an equivalent level of immunocompromise. (COVID-19 Vaccines Updated FDA EUA Gave CDC Wiggle Room In Defining Population For Third Shot) That additional dose is to be given at least 28 days after completion of the primary series.

In addition, individuals ages ≥65 years, and those ages 18-64 at increased risk of COVID-19 due to underlying health conditions or occupational/institutional exposure, are eligible for a booster dose of Pfizer/BioNTech at least six months after the primary series. (Walensky Defends Decision To Go Against Advisors On Pfizer COVID Booster Recommendation)

At this time, however, neither an additional dose for immunocompromised individuals or a booster dose is recommended for the 5-11 age group.

When asked about the absence of a recommendation for an additional dose for immunocompromised children, Woodworth said: “We do certainly recognize that this will be a recommendation that we continue to evaluate and hope to have additional data in the coming months in order to … make a more informed recommendation, but at this time they would not be recommended.”

Pfizer’s Phase II/III study in the 5-11 age group excluded children who are immunocompromised.

“We are conducting a study in immunocompromised children which will expand the whole age group from two years of age all the way to 18, and depending on the age group we will have different doses according to what has been now” authorized, Gurtman said. “So hopefully we have that data in the future, and that study will include a third dose as a booster.”

On 2 November, Pfizer CEO Albert Bourla told CNBC said the company expects to have clinical data in the 2-≤5 year age group, using a 2 mcg dose, by the end of the year.

[Derrick Gingery contributed to this story.]

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