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Covid Shots for Youngest Kids Demand Clear Messaging by Doctors

June 30, 2022, 9:30 AM

Pediatricians and their health-care systems are preparing to head off confusion about how many Covid-19 vaccine doses infants and toddlers need as they aim to ramp up inoculations for the youngest Americans.

That includes preparing for the possibility that mixing and matching of vaccines may be necessary at times.

The Centers for Disease Control and Prevention opened the door to shots for the last remaining age group with its recommendation this month in favor of vaccinating children six months up to 4 years old.

It’s also the first time the two available messenger RNA vaccines each require a different number of doses for a similar age range—for the youngest kids, it’s three shots for Pfizer Inc.'s and two for Moderna Inc.'s. The initial rollout of vaccines from Pfizer and Moderna had similar safety data and the same number of doses spread out by roughly the same amount of time.

All the doses in the primary vaccination series ideally should be the same product, the Centers for Disease Control and Prevention recommends.

But Jason G. Newland, a pediatric infectious disease physician at Washington University School of Medicine in St. Louis, said that’s not always going to be possible. A parent may show up to a vaccination site for a follow-up shot that only has Moderna on hand when their child received Pfizer the first time.

“It is going to be easiest if they pick one and stick with that one. And frankly, we know that’s not going to happen,” Newland said during a briefing by the Infectious Diseases Society of America.

The CDC clarified in its guidelines that any infants or toddlers who receive a mix of the Pfizer and Moderna vaccines should get three shots. Only those who get Moderna both times would need just two.

“Children ages 6 months–4 years who receive different mRNA products for the first 2 doses of an mRNA COVID-19 vaccine series should follow a 3-dose schedule. A third dose of either mRNA vaccine should be administered at least 8 weeks after the second dose to complete the 3-dose primary series.” the CDC said.

The Food and Drug Administration has already given the green light on mixing and matching booster shots for adults. Preliminary data from the National Institutes of Health indicate that mixing vaccines may provide even stronger protection than using the same shot across the board.

“We’ve done the mixing and matching, Newland said. “The key is that these mRNA vaccines work. They’re safe.”

Tina Q. Tan, an infectious disease pediatrician at Northwestern University’s medical school, expressed similar thoughts.

“In the adult population, you can mix and match if you have to. So I think it’s going to be probably the same thing in the pediatric population,” she said in an interview. “If they go to say, one practice, and they get X vaccine. And then say they move out of town, and they have Y vaccine, they’re probably going to have to use whatever that practice has.”

Pediatric Vaccine Schedule

The schedule for Moderna’s pediatric vaccine is two shots administered four to eight weeks apart for children six months to 17 years.

Pfizer’s vaccine schedule for children six months to 4 years requires three shots as part of the primary series, with three to eight weeks between the first and second shot and at least eight weeks to receive the third dose.

The administration of Pfizer’s vaccine for 5 -to 17-year-olds also includes three shots, but the third is a booster. Like the infant and toddler vaccine, there should be a three- to eight week gap between the first and second shot, with the booster at least five months later.

“It’s going to be important for pediatricians and for families to understand that the dosing is different, and there will be opportunities for confusion there,” C. Buddy Creech, a pediatric infectious disease physician at Vanderbilt University, said during the IDSA briefing.

“What’s going to help parents is if the child is in a situation where they need to be fully protected very quickly, that might give the nod to Moderna,” Creech, who is also the president of the Pediatric Infectious Diseases Society, said.

“If time is not so much of an issue, or Pfizer is the one that’s available, Pfizer’s a great vaccine that will also result in very good immune responses, Creech said.

Conversations Abound

Sally H. Goza, a past president of the American Academy of Pediatrics who sees patients in Fayetteville, Ga., said there are lots of conversations happening among pediatricians about which vaccine makes the most sense for their office.

“The three shots versus two is not a deal breaker for most people because it’s also 56 days from the second dose to the third dose,” she said, while acknowledging that extra shots may be the difference for some.

“That really varies amongst families. We actually started giving the Pfizer dose last week, and we’ve not had anybody be upset about that. They’re like, ‘That’s great. Well, we’ll take what you got,’” Goza said.

Pfizer ultimately landing on a third dose underscores the system for evaluating vaccines really does work, Tan said.

“When they found that the two doses didn’t give the optimal immune response in the 2- to 4-year-olds, that’s why they went to three doses,” she said. “The checks and balances work so that we’re able to put out a vaccine that’s safe and effective for whichever age group.”

Creech said he expects Moderna’s pediatric vaccine to require boosters down the line, the same way that Pfizer’s does. “There’s going to be some continued tweaking of these regimens.”

To contact the reporter on this story: Jeannie Baumann in Washington at

To contact the editors responsible for this story: Brent Bierman at; Alexis Kramer at