A new study published in the New England Journal of Medicine has evaluated the effectiveness of the Pfizer-BioNTech vaccine in children ages 5-11 during the Omicron wave, and in adolescents ages 12-18 during both the Delta and the Omicron periods. The scientists found that vaccination with a primary series of Pfizer shots reduced the risk of COVID-19-related hospitalizations in children by two-thirds during the Omicron wave.
Among vaccinated adolescents, protection against hospitalization was lower during the Omicron period than during the Delta period (as it happened in the case of adults too). However, levels of protection against highly severe cases remained high in vaccinated adolescents during both waves.
“Our study results are reassuring that COVID-19 vaccination in eligible children and adolescents continues to protect against the most severe outcomes associated with COVID-19, regardless of variant type,” said study co-author Bria Coates, a critical care physician at the Ann & Robert H. Lurie Children’s Hospital of Chicago and assistant professor of Pediatrics at Northwestern University.
“It is difficult to predict whether the vaccine will be as effective against the current subvariant of Omicron, but most likely the level of protection would be similar. Our results reinforce the importance of COVID-19 vaccination, including receiving a booster dose for those ages 12 years and older, to protect against critical illness.”
According to Dr. Coates and her colleagues, during the Omicron period (December 19, 2021 – February 17, 2022), vaccination reduced the risk of hospitalization by 68 percent in children between 5 and 11. Since vaccination for this age group was not available during the Delta period, no comparative studies could be performed.
However, for adolescents ages 12-18, protection against hospitalization declined from 92 percent during the Delta period (July 1, 2021 – December 18, 2021) to only 40 percent during the Omicron wave. Yet, protection against critical cases of COVID-19, requiring life-supporting interventions, remained high for adolescents during both Delta (96 percent) and Omicron (79 percent).
During the Delta period, protection against hospitalization in adolescents remained consistent for over six months after receipt of a primary vaccination series. Although they were lower, the levels of protection against Omicron also stayed consistent over time after vaccination.
“This consistency in vaccine effectiveness during each variant suggests that the decline in protection among adolescents between the Delta and Omicron periods might be because the Omicron variant is more likely to escape control by the immune system, rather than waning immunity since vaccination,” explained Dr. Coates. “However, more data are needed to answer this question.”