Studies Show Pfizer Vaccine May Not Protect Against COVID Infection in Kids 5–11

Recent studies show that the low-dose Pfizer COVID-19 vaccines are less effective against new cases and hospitalizations in children aged 5 to 11. This raises the question of whether Pfizer should increase its dosage for young kids.

With limited data, experts said the vaccines are still working as they were intended, and parents and caregivers should continue to vaccinate their children to the extent possible.

A preprint study from the New York State Department of Health found that Pfizer’s vaccine effectiveness was substantially lower in children ages 5–11 compared to those ages 12–17. After reviewing new cases and hospitalization rates in New York State, researchers found that Pfizer’s vaccine efficacy against infection for kids ages 5–11 declined from 65% to 12% about a month after vaccination.

The Centers for Disease Control and Prevention (CDC) on Wednesday also released data showing that the Pfizer vaccine is less effective for this age group. Based on a relatively small sample size, the CDC report found that Pfizer’s vaccine efficacy for kids 5–11 declined to 46% against urgent care visits and 74% against hospitalizations, within about two weeks to two months after vaccination.

Takeaways and Limitations 

Both studies had limited data. Researchers were also unable to control for whether a child was wearing a face mask or practicing other safety measures after getting vaccinated.

Judith Flores, MD, a pediatrician and a fellow at the American Academy of Pediatrics, told Verywell that a lot of factors weren’t considered in the New York State study.

“It’s a good ‘clue’ that we can learn from. It’s valuable information, but it’s not complete,” Flores said.

Additionally, in the CDC report, the authors noted that data from some age groups was taken in the previous wave of COVID surges and that new information was lacking for the Omicron wave.

“Infections in Omicron are very different from Delta and others. We saw protection from these vaccines less than we would hope because they weren’t designed around the Omicron variant,” Flores said, adding that the vaccines did prevent hospitalizations and deaths as intended.

Vaccine Dosage by Age Group

Children inoculated with the Pfizer vaccine received different dosages depending on their age. Kids ages 5–11 were given one-third of the dose given to people ages 12 and above.

According to the New York State researchers, the dosage difference in age groups had a big effect on vaccine effectiveness, particularly when comparing results between 11-year-olds and 12-year-olds. During one of the weeks while data was collected, vaccine efficacy against new cases for 12-year-olds was at 67%, but it dropped to 11% for 11-year-olds.

The results showed a stark difference in efficacy between close ages. But specifying different doses for children older or younger than 12 is common in the vaccine world, Flores said. This is because young children tend to have very strong immune systems, but that changes as they mature, she added.

Since vaccine manufacturers tend to work with respect to the “Goldilocks effect”—an attempt to give the smallest dose possible to protect against disease—children under the age of 12 are recommended a lower dose, Flores explained.

Whether the CDC and NY findings are strong enough to warrant an increase in dosage is unclear, though other protection methods, such as additional doses or variant-inclusive vaccines, may be prioritized first, Flores said.

“It’s clear to me as a practitioner that we’re going to get bigger and better and more effective vaccines coming in the next year,” Flores said. “That doesn’t mean that people should not vaccinate their children [now]—They should vaccinate their children, because this is the best protection we have.”

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.