Features of COVID-19 in Children During the Omicron Wave Compared With Previous Waves in Madrid, Spain

To the Editors:

The SARS-CoV-2 variant Omicron (B.1.1.529) replaced other variants in Spain during the sixth wave, accounting for 79%–94% of positive samples in the last 2 weeks of 2021.¹ The information is scarce about Omicron severity in children.

To describe the features of children with COVID-19 during the Omicron wave, we reviewed charts from children with COVID-19 attended at the emergency room of a secondary center in Spain from December 20, 2021, to January 2, 2022. All patients’ charts were reviewed 1 week after diagnosis to check complications.

The detection by reverse transcriptase-polymerase chain reaction (RT-PCR) used as target genes ORF1ab and N of the SARS-CoV-2 genome. All samples with a cycle threshold (Ct) <25 were analyzed with a second RT-PCR with probes targeting the gen S mutations consistent with Omicron. This study is part of the study EPICO-AEP.²

A total of 1,360 children were attended at the emergency room during the study period. Globally, 94 (6.9%) had a positive RT-PCR for SARS-CoV-2, with a median age of 6.5 years (interquartile range: 1.3–9.7), and 82.9% had fever. Of them, 15 (16.0%) had a Ct <25: 13/15 (86.7%) were identified as Omicron and 2/15 (13.3%) as Delta variant.

Only 2 of 94 (2.1%) patients were hospitalized: a 3-year-old girl with features of bacterial pneumonia and confirmed Omicron variant, and a 40-day-old infant with whooping cough. No patient needed pediatric intensive care unit admission or died. In a study performed by our group during the third wave, caused predominantly by the Alpha variant, 3/75 (4.0%) children with COVID-19 were hospitalized, not differently to the Omicron wave (P = 0.394), and one child needed pediatric intensive care unit admission.

To better describe the profile of children with Omicron, we identified 17 further children with Omicron attended at another center. We compared the features of the 109 ambulatory children attended during the Omicron wave in these 2 centers to 546 ambulatory children attended in previous waves in 35 centers, from March 2020 to October 2021, included in the national COVID-19 EPICO-AEP registry (Table 1).² During the Omicron wave, more children presented upper respiratory tract infection, but fewer children had pneumonia. Fever, headache, and diarrhea were more common during the Omicron wave.

TABLE 1.

Comparison Between Features of Ambulatory Children Attended During the Omicron Wave and Previous Waves at the Emergency Rooms

Features	Previous Waves N = 546 (%)	Omicron Wave N = 109 (%)	P
Sex (female)	289 (52.9%)	60 (55.0%)	0.686
Age (yrs), median (IQR)	5.7 (1.1–11.7)	6.6 (1.3–9.8)	0.330
Age band (yrs)			<0.001
0–4	259 (47.4%)	47 (43.1%)
5–12	162 (29.7%)	54 (49.5%)
12 or above	125 (22.9%)	8 (7.3%)
Comorbidity	99 (18.1%)	12 (11.0%)	0.070
Contact with household confirmed case	240 (44.0%)	33 (30.3%)	0.008
Symptoms/signs
Fever	371 (67.9%)	90 (82.6%)	0.002
Cough	264 (48.4%)	61 (56.0%)	0.147
Sore throat	99 (18.1%)	20 (18.3%)	0.957
Runny nose	197 (36.1%)	49 (45.0%)	0.081
Fatigue, malaise	73 (12.2%)	12 (11.0%)	0.728
Wheezing	23 (4.2%)	2 (1.8%)	0.237
Headache	88 (16.1%)	35 (32.1%)	<0.001
Myalgia	48 (8.8%)	4 (3.7%)	0.071
Diarrhea	75 (13.7%)	23 (21.1%)	0.049
Vomiting	91 (16.7%)	23 (21.1%)	0.265
Syndromic diagnosis*
Upper respiratory tract infection	195 (37.0%)	73 (67.0%)	<0.001
Flu-like	80 (15.2%)	14 (12.8%)	0.532
Fever without a source	84 (15.9%)	5 (4.6%)	0.002
Gastroenteritis	40 (7.6%)	7 (6.4%)	0.671
Pneumonia	38 (7.2%)	1 (0.9%)	0.013
Asymptomatic	44 (8.3%)	3 (2.8%)	0.042
Bronchitis/asthma flare	18 (3.4%)	2 (1.8%)	0.389
Bronchiolitis	2 (0.4%)	0 (0.0%)	0.519

Categorical variables are compared using the χ² or Fisher tests, and continuous variables using Wilcoxon rank-sum test. Significant P values (<0.05) are in bold.

^*The syndromic diagnosis was not recorded in 19 cases diagnosed in previous waves; percentages and P values are calculated omitting those cases.

Notably, most patients during the Omicron wave were ≤11 years old. Nearly 83% of adolescents ≥12 years old are vaccinated in Spain, which may explain the low proportion of adolescents in our population. Some studies reported that around 1%–2% of children with COVID-19 need hospitalization, likewise our study.^3,4

This study suggests that children with the Omicron variant do not have a worse outcome than children with previous variants. Omicron in children seemed to have a similar clinical profile but with increased tropism for the upper airway and less tropism for the lungs.

ACKNOWLEDGMENTS

We thank all the patients and families for their participation in this cohort, the staff members who cared for them at their personal risk in this time of epidemics and pediatricians who cared for the patients and helped gathering data including: Teresa Reinoso, Alfonso Cañete and Ane Plazaola (Hospital Universitario Infanta Sofía), David Melero, Angela Somodevilla and Raquel Guillén (UR Salud).