Study Evaluates Pfizer-BioNTech Vaccine Efficacy During Delta and Omicron Periods in Children 5-18 Years Old



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The results of a new multicenter study published in the New England Journal of Medicine found that vaccination with a primary series of Pfizer-BioNTech’s COVID-19 mRNA vaccine reduced the risk of COVID-19-associated hospitalizations by two-thirds in children aged 5 to 11 years during the Omicron period. Among adolescents aged 12 to 18 who were vaccinated with a primary series of Pfizer-BioNTech vaccines, protection against COVID-19-associated hospitalization during the Omicron period was lower than during the Delta period, similar to what which had previously been shown in adults. Levels of protection against critical COVID-19 requiring life-saving interventions remained high among adolescents vaccinated during the Delta and Omicron periods.

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“The results of our study provide reassurance that vaccination against COVID-19 in eligible children and adolescents continues to protect against the most severe outcomes associated with COVID-19, regardless of the type of variant,” said said study co-author Bria Coates, MD, critical care physician at Ann & Robert H. Lurie Children’s Hospital of Chicago and assistant professor of pediatrics at Northwestern University Feinberg School of Medicine. “It is difficult to predict whether the vaccine will be as effective against the current Omicron subvariant, but the level of protection would most likely be similar. Our results reinforce the importance of vaccination against COVID-19, including the receiving a booster dose for people aged 12 and over, to protect against serious illnesses.

During the Omicron period (December 19, 2021 to February 17, 2022), vaccination reduced the risk of hospitalization associated with COVID-19 by 68% in children aged 5 to 11 years. Vaccine efficacy against any type of hospitalization associated with COVID-19 in adolescents 12-18 years of age who received a primary series increased from 92% during the Delta period (July 1, 2021 to December 18, 2021) to 40% during the Omicron period. Protection against life-saving COVID-19 remained high for adolescents during Delta (96%) and Omicron (79%).

Due to the small number of hospitalized children aged 5 to 11 in the study, researchers were unable to analyze vaccine effectiveness by disease severity for this age group, but will continue. to be monitored as this data is collected. Data for this age group was not available for the Delta period, as younger children were not eligible for the vaccine at that time.

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Protection against hospitalization in adolescents during the Delta period remained constant for more than 6 months after receipt of a primary series. Protection levels during Omicron, although lower, also remained constant over time after the end of the primary series.

“This consistency in vaccine efficacy over each variant suggests that the drop in protection in adolescents between the Delta and Omicron periods could be due to the fact that the Omicron variant is more susceptible to escape the control of the immune system, rather than waning immunity since vaccination,” said Dr. Coates, who is also a Crown family researcher in developmental biology. “However, more data is needed to answer this question.”

Sara H. Byrd