COVID vaccine less effective against Omicron in younger kids, study shows

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Two shots of the Pfizer-BioNTech COVID-19 vaccine were less effective at curbing the risk posed by the Omicron variant in younger children compared to older age groups, according to new data published this week by the Centers for Disease Control and Prevention. 

Figures published late Thursday by the CDC from its COVID-NET hospital surveillance show that rates of COVID-19 hospitalizations were lower through the end of January among vaccinated Americans of any age, compared to the unvaccinated.

However, the smallest gaps were among children ages 5 to 17 years old. Hospitalization rates were six times higher in unvaccinated adults compared to the vaccinated. Rates were three times higher in unvaccinated 5- to 11-year-olds and two times higher in unvaccinated 12- to 17-year-olds.

The CDC also published a new study Friday in its Morbidity and Mortality Weekly Report estimating that two shots of the Pfizer vaccine was 31% effective against Omicron variant infections in children ages 5 to 11.  

Vaccine effectiveness among adolescents ages 12 to 15 against Omicron was virtually double that, at 59%, though the study’s authors cautioned that “wide and overlapping” statistical uncertainty around the two figures suggested that they “might not be significantly different.” 

Researchers regularly tested children enrolled across four states — Arizona, Florida, Texas, and Utah — starting in July 2021. During the time of the Delta variant’s dominance, the study found vaccine effectiveness among adolescents was 87% against infection. 

“Other pediatric vaccine effectiveness studies relied on lab testing data or health records and generally captured only cases where a child had symptoms and received health care. With increased use of home rapid testing, studies like ours are needed to provide more comprehensive information on rates of infection and vaccine effectiveness,” said principal investigator Lauren Olsho in a release from Abt Associates, whose scientists co-authored the study. 

Vaccinated children in the study population who did catch COVID spent on average a half day time less sick in bed, compared to the unvaccinated children who got sick. However, the study’s authors also noted that the two groups reported behaving differently: vaccinated children were more likely to say they wore face masks and reported missing more days of school when sick. 

A growing number of studies have found declining vaccine effectiveness during the Omicron period in people who have not received a booster shot, including among children

Pfizer and BioNTech have said they expect to have data from their trials early next month that could allow regulators to greenlight a third dose for children. 

In a statement, the CDC said the agency continues to recommend COVID-19 vaccination as “a safe and critical tool to protect children and teens regardless of their health status.”

While children 5 to 17 years old are generally less likely to be hospitalized with COVID-19 than adults, hundreds of kids have died from the disease and many more have faced severe complications from COVID-19. 

The CDC recently said parents may be able to space out their children’s first two shots as much as eight weeks, as a way to potentially boost vaccine effectiveness and reduce the risk of rare heart inflammation side effects linked to the vaccine.

A separate study co-authored by CDC scientists released Friday — which was posted as a preprint that has not yet been peer-reviewed — found that rates of hospitalization during COVID-19 among children overall exceeded that from earlier flu seasons, even before the record Omicron wave that drove a record surge in hospitalizations of children. 

However, the Biden administration has so far struggled to persuade many parents to vaccinate their youngest eligible children, with the early rollout having lagged that of older ages.

Only about 26.6% of children 5 to 11 years old are fully vaccinated

Through the end of January, an ongoing CDC survey found the share of parents saying they “probably or definitely” will not get their 5- to 11-year-old child vaccinated had climbed to 31%. 

“Data show that vaccines are one of the most effective ways to keep people, including children, safe from COVID-19 by preventing serious illness, hospitalization, and death,” Dr. Nirav Shah, Maine’s top health official and president of the Association of State and Territorial Health Officials said last week.

Shah’s statement came after Florida’s surgeon general sparked controversy by moving to discourage getting children vaccinated against COVID-19.

“Now is the time to help more families and communities protect themselves through vaccination,” said Shah.

© 2020 CBS Interactive Inc. All Rights Reserved.

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