The Pfizer/BioNTech COVID-19 vaccine was less effective against the Omicron than Delta variant in children and adolescents, a multi-center study suggested.
During Omicron, vaccine effectiveness (VE) in those ages 12 to 18 years was 40% (95% CI 9-60) against COVID-related hospitalization and 79% (95% CI 51-91) against critical cases, according to Manish Patel, MD, MSc, of the CDC in Atlanta, and colleagues.
While during the Delta wave, VE was 92% (95% CI 89-95) and 96% (95% CI 90 to 98), respectively, they reported in the New England Journal of Medicine.
In children ages 5 to 11 years, VE against hospitalization during Omicron was 68% (95% CI 42-82), lower than might be expected when compared to how the vaccine performed (against infection) in a randomized trial conducted prior to the Omicron period, noted Patel and colleagues.
"Our study provides strong evidence for the benefits of vaccination in preventing the most severe forms of disease related to the Delta and Omicron variants in children and adolescents," they said.
When the group analyzed time since vaccination, among those 12 to 18, they found that VE against hospitalization remained relatively similar even months after vaccination. During the Delta period, VE was 93% in the 2-22 weeks after full vaccination and 92% at 23-44 weeks. During Omicron, VE was lower but also remained stable, at 43% (2-22 weeks) and 38% (23-44 weeks).
"The sustained protection in the analysis according to time since vaccination during the Delta and Omicron periods among adolescents 12 to 18 years of age, with an overall lower effectiveness during the Omicron period, suggests that evasion of immunity contributed more to the decline in protection than waning immunity," Patel and colleagues wrote.
Previous studies done in adult populations found similarly reduced protection from the Pfizer/BioNTech vaccine against Omicron.
Studies on VE can help determine "whether observed declines are related to waning protection that would be bolstered by booster doses of current vaccines (or increasing antigen content) or are instead related to immune evasion, which might require other strategies, such as updates to the vaccine strain," Patel and colleagues said.
The current study did not evaluate booster effectiveness in children since they were only recently approved for children ages 12 to 15, the researchers said.
The study included 2,812 children, 26% of whom were fully vaccinated. COVID patients as well as their matched COVID-negative controls were from 31 pediatric hospitals from 23 U.S. states. Case patients were those hospitalized with COVID-19 as their primary reason for admission or with symptoms consistent with COVID-19 and who had a positive PCR test. Patients were excluded if they were vaccinated 0 to 13 days prior to symptom onset, admitted to the hospital for other reasons, or received a booster dose.
Of the 1,185 COVID patients, one quarter had critical COVID-19 and 14 died. Just over 90% of those with critical COVID were unvaccinated. Broken down by age group, 918 of the COVID patients were ages 12 to 18 years (median 16) and 267 were ages 5 to 11 years (median 8).
For the older group with COVID, 684 were admitted during the Delta period, 234 during the Omicron period, and 78% had at least one underlying health condition. For the younger group, who were only studied during the Omicron period, 82% had at least one underlying condition.
The researchers noted they had limited follow-up time for the children ages 5 to 11, as vaccines were only approved in late October 2021 for this age group.
Disclosures
The study was funded by the CDC.
Patel disclosed no relationships with industry.
Primary Source
New England Journal of Medicine
Source Reference: Price AM, et al "BNT162b2 protection against the omicron variant in children and adolescents" New Engl J Med 2022; DOI: 10.1056/NEJMoa2202826.
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