COVID-19–Associated Hospitalizations Among U.S. Infants Aged <6 Months — COVID-NET, 13 States, June 2021–August 2022

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COVID-19–associated hospitalization rates are highest among adults aged ≥65 years (1); however, COVID-19 can and does cause severe and fatal outcomes in children, including infants (2,3). After the emergence of the SARS-CoV-2 B.1.1.529 (Omicron) BA.1 variant in December 2021, hospitalizations among children aged <5 years, who were ineligible for vaccination, increased more rapidly than did those in other age groups (4). On June 18, 2022, CDC recommended COVID-19 vaccination for infants and children aged ≥6 months (5). Data from the Coronavirus Disease 2019–Associated Hospitalization Surveillance Network (COVID-NET)* were analyzed to describe changes in the age distribution of COVID-19–associated hospitalizations since the Delta-predominant period (June 20–December 18, 2021)^† with a focus on U.S. infants aged <6 months. During the Omicron BA.2/BA.5–predominant periods (start highlightMarch 20end highlight–August 31, 2022), weekly hospitalizations per 100,000 infants aged <6 months increased from a nadir of 2.2 (week ending April 9, 2022) to a peak of 26.0 (week ending July 23, 2022), and the average weekly hospitalization rate among these infants (13.7) was similar to that among adults aged 65–74 years (13.8). However, the prevalence of indicators of severe disease^§ among hospitalized infants did not increase since the B.1.617.2 (Delta)-predominant period. To help protect infants too young to be vaccinated, prevention should focus on nonpharmaceutical interventions and vaccination of pregnant women, which might provide protection through transplacental transfer of antibodies (6).

COVID-NET conducts population-based surveillance for laboratory-confirmed COVID-19–associated hospitalizations among residents of predefined surveillance catchment areas.^¶ COVID-19–associated hospitalizations are defined as receipt of a positive SARS-CoV-2 molecular or rapid antigen detection test result during hospitalization or during the 14 days preceding hospital admission. Demographic data were collected on all COVID-19–associated hospitalizations in 13 states and used to calculate age-stratified hospitalization rates.** Clinical data (signs and symptoms at admission,^†† underlying medical conditions, and indicators of severe disease) were available for infants aged <6 months from 12 states.^§§ Using previously described methods (4), clinical data were collected on all infant COVID-NET cases. Because of the surge in hospitalizations during December 2021 and January 2022, some sites abstracted clinical data on a representative sample of hospitalized infants.^¶¶ A birth hospitalization was defined as the hospitalization during which the infant was born.

This analysis describes weekly COVID-19–associated hospitalization rates (hospitalizations per 100,000 population) and clinical characteristics of infants aged <6 months during June 20, 2021–August 31, 2022, which includes SARS-CoV-2 Delta (June 20–December 18, 2021), Omicron BA.1 (December 19, 2021–March 19, 2022), Omicron BA.2 (March 20–June 18, 2022), and Omicron BA.5 (June 19–August 31, 2022) variant–predominant periods. Hospitalization rates from the pre-Delta period and among all other age groups are included for comparison. Average weekly rates and demographic and clinical characteristics of infants aged <6 months were compared across variant-predominant periods. Unadjusted weekly COVID-19–associated hospitalization rates were calculated by dividing the total number of hospitalized patients by population estimates within each age group for the counties included in the surveillance catchment area.*** Because population estimates are available in 1-year age increments, population denominators for hospitalization rates among infants aged <6 months were calculated as one half the population estimate for infants aged <1 year. Three-week moving averages are presented for visualization purposes. Rate ratios (RRs) and 95% CIs were calculated. Demographic characteristics, clinical outcomes, and severity across SARS-CoV-2 variant-predominant periods were compared; the Omicron BA.2- and BA.5-predominant periods were combined in analyses because of small sample sizes. During the combined Omicron BA.2/BA.5-predominant period, the proportions of hospitalized infants with underlying medical conditions and symptoms on admission by age group (<1 month, 1–3 months, 4–5 months) were estimated. Wilcoxon rank-sum tests and chi-square tests were used to compare medians and proportions, respectively; p-values <0.05 were considered statistically significant. Percentages were weighted to account for the probability of selection for sampled cases, and further adjusted to account for nonresponse (i.e., an incomplete chart review). Data were analyzed using SAS (version 9.4; SAS Institute). This activity was reviewed by CDC and conducted consistent with applicable federal law and CDC policy.^†††

During the Omicron BA.2/BA.5-predominant period, the weekly hospitalization rate among infants aged <6 months increased elevenfold (95% CI = 4.3–33.3) from a nadir of 2.2 (week ending April 9, 2022) to a peak of 26.0 (week ending July 23, 2022) and began to decline thereafter (Figure). The mean weekly hospitalization rate in this group was higher during the Omicron BA.2/BA.5 period (13.7) than during the Delta period (8.3) (RR = 1.6; 95% CI = 1.4–1.8). Compared with the Delta period, rates were also higher during the BA.2/BA.5 period among infants and children aged 6 months–4 years (RR = 1.9) and adults aged ≥75 years (RR = 1.4) but lower among children and adolescents aged 5–17 years (RR = 0.9), adults aged 18–64 years (RR = 0.5), and adults aged 65–74 years (RR = 0.8). The mean weekly hospitalization rate among infants aged <6 months during the Omicron BA.2/BA.5 period (13.7) was less than that of adults aged ≥75 years (39.4), similar to that of adults aged 65–74 years (13.8) and higher than rates in all other pediatric age groups (2.3 and 0.8 for children aged start highlight6 months–4 years and 5–17 yearsend highlight, respectively) and in adults aged <65 years (start highlight4.6end highlight).

Complete clinical data were available for 1,116 infants aged <6 months hospitalized with laboratory-confirmed COVID-19, including 321, 322, and 473 infants hospitalized during the Delta, Omicron BA.1, and Omicron BA.2/BA.5 periods, respectively (Table 1). Differences during the three periods were small, and not all were statistically significant; however, indicators of severity, including length of hospital stay, and the proportion of hospitalizations that required intensive care unit admission, high-flow nasal cannula, mechanical ventilation, or bilevel positive airway pressure/continuous positive airway pressure (BiPAP/CPAP) were consistently lower during the Omicron BA.2/BA.5 period than during the Delta period, and in-hospital deaths were rare (<1%).

Among 473 infants aged <6 months hospitalized during the Omicron BA.2/BA.5 variant-predominant period, 397 (84%) had COVID-19–related symptoms. Among all 473 infants, 174 (38%) were aged <1 month; 69 (39%) of these were birth hospitalizations (Table 2). Among infants who received a positive SARS-CoV-2 test result during the birth hospitalization, 60 (87%) were asymptomatic. Excluding birth hospitalizations, similar proportions were hospitalized with COVID-19–related symptoms among infants aged <1 month (94%), 1–2 months (97%) and 3–5 months (96%). At least one underlying medical condition was present in 26% of hospitalized infants aged 1–2 months and 36% of those aged 3–5 months. Prematurity^§§§ was the most frequently reported underlying condition (20% and 25% of infants aged 1–2 months and 3–5 months, respectively). Most infants aged 1–2 months (74%) and 3–5 months (68%) had fever on admission.

Acknowledgments

Ashley Coates, Brenna Hall, Rebecca Longson, Joelle Nadle, Monica Napoles, Utsav Pokharel, California Emerging Infections Program; Nisha Alden, Sharon Emmerling, Madelyn Lensing, Jordan Surgnier, Millen Tsegaye, Colorado Department of Public Health and Environment; Ann Basting, Tessa Carter, Maria Correa, Daewi Kim, James Meek, Julie Plano, Hazhia Sorosindi, Connecticut Emerging Infections Program, Yale School of Public Health; Gracie Chambers, Taylor Eisenstein, Emily Fawcett, Annabel Patterson, Foundation for Atlanta Veterans Education and Research; Georgia Emerging Infections Program, Georgia Department of Public Health; Atlanta Veterans Affairs Medical Center; Marina Bruck, Rayna Ceaser, Sabrina Hendrick, Johanna Hernandez, Asmith Joseph, Grayson Kallas, Stephanie Lehman, Jana Manning, Allison Roebling, Suzanne Segler, Chandler Surell, Katelyn Ward, Hope Wilson; Emory University School of Medicine; Georgia Emerging Infections Program, Georgia Department of Public Health; Atlanta Veterans Affairs Medical Center; Kenzie Teno, Andrew Weigel, Iowa Department of Health and Human Services; Chloe Brown, Jim Collins, Shannon Johnson, Sue Kim, Alexander Kohrman, Lauren Leegwater, Sanchitha Meda, Alyanna Melicor, Libby Reeg, Val Tellez Nunez, Michigan Department of Health and Human Services; Kayla Bilski, Erica Bye, Kathy Como-Sabetti, Grace Hernandez, Stephanie Meyer, Kieu My Phi, Minnesota Department of Health; Cory Cline, Adrienne Domen, Melissa Judson, Sunshine Martinez, Florent Nkouaga, Kelly Plymesser, Susan L. Ropp, Jasmyn Sanchez, Chad Smelser, Daniel M. Sosin, New Mexico Department of Health; Kathy M. Angeles, Molly Bleecker, Sarah Shrum Davis, Nancy Eisenberg, Emily Hancock, Sarah A. Khanlian, Sarah Lathrop, Wickliffe Omondi, Mayvilynne Poblete, Dominic Rudin, Yadira Salazar-Sanchez, New Mexico Emerging Infections Program; Jennifer Akpo, Celina Chavez, Murtada Khalifa, Alesia Reed, Yassir Talha, CDC Foundation, New Mexico Department of Health; Adam Rowe, Jemma Rowlands, Nancy Spina, New York State Department of Health; Virginia Cafferky, Christina Felsen, Maria Gaitan, Christine Long, Thomas Peer, Kevin Popham, University of Rochester School of Medicine and Dentistry; Laurie Billing, Julie Freshwater, Denise Ingabire-Smith, Ann Salvator, Rebekah Sutter, Ohio Department of Health; Bentley Akoko, Kathy Billings, Katie Dyer, Anise Elie, Gail Hughett, Karen Leib, Terri McMinn, Danielle Ndi, Manideepthi Pemmaraju, William Schaffner, Vanderbilt University Medical Center; Ashton Bruno, Amanda Carter, Ryan Chatelain, Andrea George, Rosie Gonzalez, Andrew Haraghey, Mary Hill, Kristen P. Olsen, Emily Roberts, Courtney H. Sacco, Holly Staten, Ashley Swain, Salt Lake County Health Department; Onika Anglin, National Center for Immunization and Respiratory Diseases, CDC.

Corresponding author: Sarah Hamid, tsl4@cdc.gov.

¹National Center for Immunization and Respiratory Diseases, CDC; ²Epidemic Intelligence Service, CDC; ³Division of Birth Defects and Infant Disorders, National Center on Birth Defects and Developmental Disabilities, CDC; ⁴California Emerging Infections Program, Oakland, California; ⁵Career Epidemiology Field Officer Program, CDC; ⁶Colorado Department of Public Health and Environment; ⁷Connecticut Emerging Infections Program, Yale School of Public Health, New Haven, Connecticut; ⁸Emory University School of Medicine, Atlanta, Georgia; ⁹Georgia Emerging Infections Program, Georgia Department of Public Health; ¹⁰Atlanta Veterans Affairs Medical Center, Atlanta, Georgia; ¹¹Michigan Department of Health and Human Services; ¹²Minnesota Department of Health; ¹³New Mexico Emerging Infections Program, University of New Mexico, Albuquerque, New Mexico; ¹⁴New York State Department of Health; ¹⁵University of Rochester School of Medicine and Dentistry, Rochester, New York; ¹⁶Ohio Department of Health; ¹⁷Oregon Health Authority; ¹⁸Vanderbilt University Medical Center, Nashville, Tennessee; ¹⁹Salt Lake County Health Department, Salt Lake City, Utah.

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FIGURE. Weekly COVID-19–associated hospitalization rates* by age group (3-week moving average) and period of SARS-CoV-2 variant predominance^† — Coronavirus Disease 2019–Associated Hospitalization Surveillance Network, 13 states,^§ March 2020–August 2022

* Number of patients with a laboratory-confirmed COVID-19–associated hospitalization per 100,000 population. Rates are calculated using the CDC National Center for Health Statistics’ vintage 2020 bridged-race postcensal population estimates for the counties included in the surveillance area (https://www.cdc.gov/nchs/nvss/bridged_race.htm). Rates are subject to change as additional data are reported.

^† Periods of SARS-CoV-2 variant predominance are defined as follows: Delta: June 20–December 18, 2021; Omicron BA.1: December 19, 2021–March 19, 2022; Omicron BA.2: March 20–June 18, 2022; and Omicron BA.5: June 19–August 31, 2022.

^§ Data are collected in selected counties in California, Colorado, Connecticut, Georgia, Maryland, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee, and Utah. A list of these counties is available at https://www.cdc.gov/mmwr/volumes/69/wr/mm6915e3.htm. Additional information on surveillance methods is available at https://www.cdc.gov/coronavirus/2019-ncov/covid-data/covid-net/purpose-methods.html.

Abbreviations: BiPAP/CPAP = bilevel positive airway pressure/continuous positive airway pressure; COVID-NET = Coronavirus Disease 2019–Associated Hospitalization Surveillance Network; ICU = intensive care unit; NA = not applicable; NH = non-Hispanic.
* Data are a weighted sample of hospitalized infants with completed medical record abstractions. Sample sizes presented are unweighted with weighted percentages.
^† Includes infants admitted to a hospital with an admission date during June 20, 2021–August 31, 2022, in 12 states participating in COVID-NET: California, Colorado, Connecticut, Georgia, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee, and Utah. https://www.cdc.gov/mmwr/volumes/69/wr/mm6915e3.htm
^§ Proportions between the Delta variant and Omicron BA.2/BA.5 variant periods of predominance were compared with chi-square tests, and medians were compared with the Wilcoxon rank-sum test, accounting for sampling weights.
^¶ If ethnicity was unknown, NH ethnicity was assumed.
** Includes NH persons reported as other or multiple races and persons of Alaska Native and American Indian race.
^†† Hospitalization outcomes are not mutually exclusive.
^§§ Relative SE >30%.

Abbreviation: COVID-NET = Coronavirus Disease 2019–Associated Hospitalization Surveillance Network.
* Data are from a weighted sample of hospitalized infants with completed medical record abstractions. Sample sizes presented are unweighted with weighted percentages.
^† Includes infants admitted to a hospital with an admission date during June 20, 2021–August 31, 2022, in 12 states participating in COVID-NET: California, Colorado, Connecticut, Georgia, Michigan, Minnesota, New Mexico, New York, Ohio, Oregon, Tennessee, and Utah. https://www.cdc.gov/mmwr/volumes/69/wr/mm6915e3.htm
^§ A birth hospitalization was defined as the hospitalization during which the infant was born.
^¶ Defined as one or more of the following: prematurity, neurologic disorders, congenital heart disease, abnormality of airway, chronic metabolic disease, immunocompromised condition, chronic lung disease of prematurity/bronchopulmonary dysplasia, or asthma/reactive airway disease. Underlying conditions that occurred in fewer than five sampled cases in any stratum are not displayed.
** COVID-19–related signs and symptoms included respiratory conditions (congestion/runny nose, cough, shortness of breath/respiratory distress, upper respiratory infection, wheezing, nausea/vomiting, rash, and seizures) and nonrespiratory conditions (conjunctivitis, diarrhea, fever/chills, apnea, cyanosis, decreased vocalization/stridor, dehydration, hypothermia, inability to eat/poor feeding, and lethargy). Signs and symptoms were abstracted from medical charts and might be incomplete.
^†† Symptoms that occurred in fewer than five sampled cases in any stratum are not displayed.
^§§ Relative SE >30%.