Discussion
The Omicron variant, which is associated with increased transmissibility and partial escape from infection- or vaccine-induced immunity, replaced Delta as the predominant variant in the United States in late December 2021.[1] Once the Omicron variant became predominant, peak population-based COVID-19–associated hospitalization rates among children and adolescents were four times as high as rates during the peak of the Delta period. Children aged 0–4 years, who were ineligible for vaccination during this time, experienced the largest increase in hospitalization rates. Observed indicators of severe COVID-19 among children and adolescents, in addition to the potential for longer-term sequelae,[4,5] highlight the importance of multicomponent strategies to reduce the incidence of COVID-19, including vaccination of eligible persons and other prevention measures.†††††
Among adolescents aged 12–17 years, the only pediatric age group for whom a COVID-19 vaccine was approved throughout the study period, December hospitalization rates among unvaccinated adolescents were approximately six times those among fully vaccinated adolescents, suggesting that vaccines were highly effective in preventing serious COVID-19 illness. Vaccination eligibility was expanded to include children aged 5–11 years on November 2, 2021. As of December 31, 2021, 54% of the population aged 12–17 years and 16% of those aged 5–11 years had completed a COVID-19 primary vaccination series.§§§§§ Increasing vaccination coverage among both age groups can reduce COVID-19–associated hospitalizations;[6] enhanced outreach strategies are needed to address disparities in vaccination coverage by race/ethnicity.
Consistent with national hospital surveillance data,[7] the findings in this report indicate that the Omicron-predominant period had higher rates of pediatric COVID-19 hospitalizations than the Delta-predominant period. No differences were found between the Delta- and Omicron-predominant periods in the proportion of hospitalizations that were likely to be related to COVID-19. Findings suggest that incidental admissions do not account for the increase in hospitalization rates observed during the Omicron period. Throughout the COVID-19 pandemic, admissions for reasons other than COVID-19 have been recorded,[8,9] and during both the Delta- and Omicron-predominant periods, incidental admissions were more likely among fully vaccinated adolescents. Reasons for admission should continue to be monitored as more children and adolescents become fully vaccinated.
The findings in this report are subject to at least six limitations. First, COVID-19–associated hospitalizations might have been missed because of testing practices and test availability. Second, the period of Omicron variant predominance with available detailed clinical data is brief (December 19–31, 2021) and does not capture the peak of hospitalizations during the Omicron period; in addition, the Delta variant was still circulating in late December. Third, accounting for seasonality in comparisons of Delta and Omicron predominant periods was not possible. Fourth, the number of hospitalized children eligible for vaccination remained low at the time of reporting, and hospitalization rates stratified by vaccination status are subject to error if misclassification of vaccination status occurred. Fifth, because children aged 5–11 years could not meet the definition for being fully vaccinated until December 7, 2021, vaccination among this age group was not considered in this study. However, vaccinations could have affected hospitalization rates during the Omicron period. Further, boosters among adolescents aged 12–17 years could not be examined because the recommendation was so recent. Finally, the COVID-NET catchment areas include approximately 10% of the U.S. population; thus, these findings might not be generalizable to the entire United States.
Coinciding with emerging predominance of the Omicron variant, rates of COVID-19–associated hospitalization among children and adolescents increased rapidly during the last 2 weeks of December 2021, especially among those aged 0–4 years. Moreover, among adolescents, hospitalization rates were higher among those who were unvaccinated. Vaccination of eligible persons, in addition to other prevention strategies such as masking, are critical to reducing the incidence of severe COVID-19 among children and adolescents.¶¶¶¶¶ All persons who are eligible for vaccination should receive and stay up to date with COVID-19 vaccines to reduce the risk for severe disease for themselves and others with whom they come into contact, including children who are currently too young to be vaccinated.******
Acknowledgments
Joelle Nadle, Sherry Quach, Jeremy Roland, Gretchen Rothrock, California Emerging Infections Program, Oakland, California; Rachel Herlihy, Madelyn Lensing, Jordan Surgnier, Millen Tsegaye, Colorado Department of Public Health and Environment; Ann Basting, Tessa Carter, Daewi Kim, Julie Plano, Connecticut Emerging Infections Program, Yale School of Public Health; Marina Bruck, Rayna Ceaser, Gracie Chambers, Taylor Eisenstein, Sabrina Hendrick, Johanna Hernandez, Asmith Joseph, Grayson Kallas, Stephanie Lehman, Jana Manning, Annabel Patterson, Allison Roebling, Suzanne Segler, Chandler Surell, Hope Wilson, School of Medicine, Emory University, Georgia Emerging Infections Program, Georgia Department of Public Health, Veterans Affairs Medical Center, Foundation for Atlanta Veterans Education and Research, Atlanta, Georgia; Chloe Brown, Jim Collins, Shannon Johnson, Sue Kim, Alexander Kohrman, Lauren Leegwater, Sierra Peguies-Khan, Libby Reeg, Michigan Department of Health and Human Services; Alison Babb, Richard Danila, Kristen Ehresmann, Jake Garfin, Jennifer Gilbertson, Grace Hernandez, Melissa McMahon, Kieu My Phi, Jill Reaney, Sara Vetter, Xiong Wang, Minnesota Department of Health; Cory Cline, Melissa Judson, Sunshine Martinez, Florent Nkouaga, Jasmyn Sanchez, Daniel Sosin, New Mexico Department of Health; Kathy M. Angeles, Molly Bleecker, Sarah Shrum Davis, Nancy Eisenberg, Sarah A. Khanlian, Sarah Lathrop, Wickliffe Omondi, Mayvilynne Poblete, Dominic Rudin, Yadira Salazar-Sanchez, New Mexico Emerging Infections Program; Jennifer Akpo, Celina Chavez, Yassir Talha, Alesia Reed, CDC Foundation, New Mexico Department of Health; Kerianne Engesser, Suzanne McGuire, New York State Department of Health; Christina Felsen, Maria Gaitan, Christine Long, Thomas Peer, University of Rochester School of Medicine and Dentistry; Julie Freshwater, Denise Ingabire-Smith, Ann Salvator, Rebekah Sutter, Ohio Department of Health; Kathy Billings, Katie Dyer, Anise Elie, Gail Hughett, Karen Leib, Terri McMinn, Danielle Ndi, Manideepthi Pemmaraju, Emmanuel Sackey, Vanderbilt University Medical Center; Ian Buchta, Amanda Carter, Melanie Crossland, Andrew Haraghey, Mary Hill, Laine McCullough, Jake Ortega, Tyler Riedesel, Caitlin Shaw, Ashley Swain, Salt Lake County Health Department, Salt Lake City, Utah; Rainy Henry, Sonja Mali Nti-Berko, Robert W. Pinner, Alvin Shultz, CDC; Mimi Huynh, Council of State and Territorial Epidemiologists.
Morbidity and Mortality Weekly Report. 2022;71(7):271-278. © 2022 Centers for Disease Control and Prevention (CDC)