key: cord-0812390-nyo66fuf authors: Delahoy, Miranda J.; Ujamaa, Dawud; Taylor, Christopher A.; Cummings, Charisse; Anglin, Onika; Holstein, Rachel; Milucky, Jennifer; O’Halloran, Alissa; Patel, Kadam; Pham, Huong; Whitaker, Michael; Reingold, Arthur; Chai, Shua J.; Alden, Nisha B.; Kawasaki, Breanna; Meek, James; Yousey-Hindes, Kimberly; Anderson, Evan J.; Openo, Kyle P.; Weigel, Andy; Teno, Kenzie; Reeg, Libby; Leegwater, Lauren; Lynfield, Ruth; McMahon, Melissa; Ropp, Susan; Rudin, Dominic; Muse, Alison; Spina, Nancy; Bennett, Nancy M.; Popham, Kevin; Billing, Laurie M.; Shiltz, Eli; Sutton, Melissa; Thomas, Ann; Schaffner, William; Talbot, H. Keipp; Crossland, Melanie T.; McCaffrey, Keegan; Hall, Aron J.; Burns, Erin; McMorrow, Meredith; Reed, Carrie; Havers, Fiona P.; Garg, Shikha title: Comparison of influenza and COVID-19–associated hospitalizations among children < 18 years old in the United States—FluSurv-NET (October–April 2017–2021) and COVID-NET (October 2020–September 2021) date: 2022-05-20 journal: Clin Infect Dis DOI: 10.1093/cid/ciac388 sha: d7772a2f7981a18bdfaa343eefe0d800b2b7bcc4 doc_id: 812390 cord_uid: nyo66fuf BACKGROUND: Influenza virus and SARS-CoV-2 are significant causes of respiratory illness in children. METHODS: Influenza and COVID-19-associated hospitalizations among children <18 years old were analyzed from FluSurv-NET and COVID-NET, two population-based surveillance systems with similar catchment areas and methodology. The annual COVID-19-associated hospitalization rate per 100 000 during the ongoing COVID-19 pandemic (October 1, 2020–September 30, 2021) was compared to influenza-associated hospitalization rates during the 2017–18 through 2019–20 influenza seasons. In-hospital outcomes, including intensive care unit (ICU) admission and death, were compared. RESULTS: Among children <18 years old, the COVID-19-associated hospitalization rate (48.2) was higher than influenza-associated hospitalization rates: 2017–18 (33.5), 2018–19 (33.8), and 2019–20 (41.7). The COVID-19-associated hospitalization rate was higher among adolescents 12–17 years old (COVID-19: 59.9; influenza range: 12.2-14.1), but similar or lower among children 5–11 (COVID-19: 25.0; influenza range: 24.3-31.7) and 0–4 (COVID-19: 66.8; influenza range: 70.9-91.5) years old. Among children <18 years old, a higher proportion with COVID-19 required ICU admission compared with influenza (26.4% vs 21.6%; p < 0.01). Pediatric deaths were uncommon during both COVID-19- and influenza-associated hospitalizations (0.7% vs 0.5%; p = 0.28). CONCLUSIONS: In the setting of extensive mitigation measures during the COVID-19 pandemic, the annual COVID-19-associated hospitalization rate during 2020–2021 was higher among adolescents and similar or lower among children <12 years old compared with influenza during the three seasons before the COVID-19 pandemic. COVID-19 adds substantially to the existing burden of pediatric hospitalizations and severe outcomes caused by influenza and other respiratory viruses. than the COVID-19-associated hospitalization rate (59.9). 4 During October 1, 2021-April 9, 2022, the preliminary COVID-19-associated hospitalization rate among 5 all children was higher than influenza-associated hospitalization rates during October-April of 2017-18 6 through 2021-22 and was also higher than the annual COVID-19-assocated hospitalization rate during 7 October 2020-September 2021 (Supplementary Figure 2A) . Increases in the COVID-19-associated 8 hospitalization rate were largely driven by increased rates among infants 0-6 months old 9 (Supplementary Figure 2B) . hospitalized with COVID-19 during October 2020-September 2021, the median age was lower for 16 influenza (3 years; interquartile range [IQR]: 1-7) than COVID-19 (9 years; IQR: 1-15) ( (Table 2) . Asthma/reactive airway disease, neurologic 2 disorder, and obesity were the most prevalent conditions for influenza and COVID-19. A higher 3 proportion of children with influenza compared with COVID-19 had asthma (23.6% vs 16.3%) or chronic 4 lung disease (6.0% vs 3.3%), but lower proportions had diabetes (1.2% vs 3.8%) or obesity (17.5% vs 5 35.0%). 6 The median hospital length of stay was lower for children with influenza compared with COVID-19 (2 vs 7 3 days, p<0.01) ( Table 2) . A higher proportion of children with influenza compared with COVID-19 had 8 pneumonia (17.8% vs 13.3%; p<0.01), but lower proportions required IMV (5.3% vs 6.2%; p=0.04) or ICU 9 admission (21.6% vs 26.4%; p<0.01). The proportion of children with influenza vs COVID-19 who died 10 during hospitalization was similar (0.5% vs 0.7%, p=0.28). 11 In sensitivity analyses, proportions experiencing severe outcomes were similar when examining the 12 following hospitalization categories: all influenza or COVID-19-associated hospitalizations, influenza or 13 COVID-19-associated hospitalizations with ≥ 1 symptom at admission (96.9% of 6774 influenza 14 hospitalizations and 79.7% of 3461 COVID-19 hospitalizations), and COVID-19-associated hospitalizations 15 with COVID-19 as the primary admission reason (74.9% of COVID-19-associated hospitalizations) (Table 16 3). Among COVID-19-associated hospitalizations, proportions with pneumonia or ICU admission 17 increased modestly with increasing age when restricted to hospitalizations with ≥ 1 symptom at 18 admission or COVID-19 as the primary admission reason. However, other severe outcomes such as IMV 19 and in-hospital death were similar across the hospitalization categories. 20 Among children <18 years old, the COVID-19-associated hospitalization rate during one year of the 22 ongoing COVID-19 pandemic was higher than influenza-associated hospitalization rates during each of 23 the three seasons before the pandemic, with differences observed by age group. Severe outcomes such 1 as ICU admission, IMV, and in-hospital death were generally similar among children with COVID-19 2 compared with influenza. Influenza has long been recognized as an important cause of severe 3 respiratory illness in children in the United States and globally [1, 18] . These data add to the growing 4 literature demonstrating that COVID-19 is also an important cause of severe disease among children. 5 Prevention measures such as physical distancing, mask usage, and virtual learning likely contributed to 6 historically low levels of influenza circulation during the 2020-21 influenza season in the United States 7 one-third of children with COVID-19 did not, and overall, one in five children with COVID-19 did not have 23 any symptoms at admission. Large proportions of children with influenza or COVID-19 had non-24 I P T respiratory symptoms, highlighting a range of symptom presentations among children hospitalized with 1 influenza and COVID-19. Relying on respiratory or febrile symptoms alone could result in missed 2 opportunities to detect influenza or SARS-COV-2 infections. Respiratory virus testing can help distinguish 3 between these viruses and guide treatment and infection prevention decisions [24] [25] [26] . There were also 4 differences in the prevalence of underlying conditions among children with influenza versus COVID-19, 5 which may in part be driven by differences in median age. The prevalence of obesity was approximately 6 double among children with COVID-19 compared with influenza. Notably, the proportion of children 7 with COVID-19 who were obese (35%) was similar to findings from another study of hospitalized 8 children with COVID-19 (32%) [27] and higher than the national obesity prevalence among persons 2-9 19 years old (22% in 2020) [28] . 10 Our analysis and others demonstrate that both influenza and COVID-19 can cause severe disease in 11 children [4, 5] . Among hospitalized children, 22% with influenza and 26% with COVID-19 required ICU 12 admission, and 5% with influenza and 6% with COVID-19 required IMV. Proportions experiencing severe 13 outcomes were generally similar when restricting to those with ≥1 symptom of influenza or COVID-19 at Influenza vaccines are safe and effective at preventing hospitalizations, and were available to children 23 ≥ 6 months old during all seasons included in this analysis [6, 30] . Based on national survey data, 24 during the COVID-19 pandemic, and differential availability of COVID-19 vaccines by age group and time-1 period could not be measured, and likely affects the comparison of influenza versus COVID-19-2 associated hospitalization rates. Fourth, only deaths occurring during hospitalizations were captured, 3 which may miss out-of-hospital deaths associated with influenza or COVID-19 [37] . Fifth, the FluSurv-4 NET and COVID-NET catchment areas include approximately 9-10% of the U.S. population and findings 5 may not be generalizable to the entire country. Last, this analysis assessed COVID-19-associated 6 hospitalization rates during a single year of the ongoing COVID-19 pandemic and did not capture rate 7 fluctuations that have occurred due to the changing epidemiology of SARS-CoV-2, including the 8 emergence of variants of concern. 9 The omicron variant of SARS-CoV-2 emerged rapidly during December 2021 and resulted in a peak 10 COVID-19 weekly hospitalization rate approximately five times as high as the peak hospitalization rate seasons. Surveillance is conducted during October 1-April 30 each season. The FluSurv-NET catchment area includes California are included. The COVID-NET catchment area includes California Data on sore throat were collected for children of all ages but reported only among children ages ≥ 3 years (for FluSurv-NET: N = 920 children ages 3-4 and N = 3788 ages 3-17 years Upper respiratory illness was included as a symptom if there was a note in the medical chart referring to a patient having "upper respiratory illness" or "influenza-like illness Other symptoms collected by COVID-NET were: myalgia, chest pain, loss of taste, loss of smell, diarrhea, conjunctivitis, fatigue, headache, rash, nausea/vomiting, abdominal pain, and hemoptysis; for children < 2 years old symptoms also included apnea, cyanosis, decreased vocalization/stridor, dehydration, hypothermia, inability to eat/poor feeding, and lethargy. Other symptoms collected by FluSurv-NET only during the 2017-18 season were: myalgia, chest pain, diarrhea, conjunctivitis, fatigue, headache, nausea/vomiting, and rash. Denominators for percentages for other symptoms for FluSurv-NET for the 2017 seasons. Surveillance is conducted during October 1-April 30 each season. The FluSurv-NET catchment area includes California are included. The COVID-NET catchment area includes California Percentages for obesity are calculated for pediatric cases with non-missing obesity data for FluSurv-NET: ages 2-4 (N = 1233) Percentages for premature are calculated for children ages 0-2 years for FluSurv-NET (N = 2986) and for COVID-NET (N = 1105) A standardized pneumonia case definition is used, which includes a combination of radiographic findings of bronchopneumonia, air space opacity, consolidation, lobar or interstitial infiltrate within 3 days of hospital admission for FluSurv-NET and at any time during hospitalization for COVID-NET, and either an ICD-10-CM-coded discharge diagnosis of pneumonia or documentation of pneumonia on hospital discharge summary P values are for the comparison of children aged 0-17 years in FluSurv-NET versus COVID-NET seasons. Surveillance is conducted during October 1-April 30 each season. The FluSurv-NET catchment area includes California are included. The COVID-NET catchment area includes California The list of symptoms collected varied by surveillance platform and year. Acute respiratory or febrile symptoms were abstracted for all FluSurv-NET seasons and for COVID-NET and are defined as fever, congestion/runny nose, cough, shortness of breath, sore throat, upper respiratory illness or influenza-like illness, and wheezing. Other symptoms abstracted for all FluSurv-NET seasons and for COVID-NET are altered mental state/confusion and seizure. Other symptoms collected by COVID-NET were: myalgia, chest pain, loss of taste, loss of smell, diarrhea, conjunctivitis, fatigue, headache, rash, nausea/vomiting, abdominal pain, and hemoptysis; for children <2 years symptoms also included apnea, cyanosis, decreased vocalization/stridor, dehydration, hypothermia, inability to eat/poor feeding, and lethargy. Other symptoms collected by FluSurv-NET during the 2017-18 season were: myalgia If the chief complaint or history of present illness documents fever/respiratory illness, COVID-19-like illness, or a suspicion for COVID-19, a case is categorized as having COVID-19 as the primary reason for admission. If the chart specifically indicates that the positive SARS-CoV-2 test was an incidental finding or that the admission was likely not COVID-19-related, the "other, specify" reason for the admission is marked and the admission is noted as "admission likely not COVID-19-related per notes". For other cases where the "other, specify" reason for admission is marked Exact 95% Confidence Intervals for binomial proportions were calculated using the Clopper-Pearson method A standardized pneumonia case definition is used, which includes a combination of radiographic findings of bronchopneumonia, air space opacity, consolidation, lobar or interstitial infiltrate within 3 days of hospital admission, and either an ICD-10-CM-coded discharge diagnosis of pneumonia or documentation of pneumonia on hospital discharge summary