Table 1.
Characteristics of cases and controls overall and separately in the catch-up and at-birth nirsevimab immunization groups, Spain, 2024/2025 season (based on data from n = 559 children)
| Characteristic | Overall (n = 559) | Catch-up immunization (n = 249) | At-birth immunization (n = 310) |
||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Cases | Controls | Cases | Controls | Cases | Controls | ||||||||||||
| N | % | N | % | N | % | N | % | N | % | ||||||||
| Number of patients | 199 | 35.6 | 360 | 64.4 | 102 | 41.0 | 147 | 59.0 | 97 | 31.3 | 213 | 68.7 | |||||
| Sex | |||||||||||||||||
| Male | 116 | 58.3 | 227 | 63.1 | 62 | 60.8 | 97 | 66.0 | 54 | 55.7 | 130 | 61.0 | |||||
| Female | 83 | 41.7 | 133 | 36.9 | 40 | 39.2 | 50 | 34.0 | 43 | 44.3 | 83 | 39.0 | |||||
| Month of birth | |||||||||||||||||
| April 2024 | 10 | 5.0 | 15 | 4.2 | 10 | 9.8 | 15 | 10.2 | NA | NA | |||||||
| May 2024 | 11 | 5.5 | 16 | 4.4 | 11 | 10.8 | 16 | 10.9 | |||||||||
| June 2024 | 6 | 3.0 | 25 | 6.9 | 6 | 5.9 | 25 | 17.0 | |||||||||
| July 2024 | 19 | 9.6 | 31 | 8.6 | 19 | 18.6 | 31 | 21.1 | |||||||||
| August 2024 | 24 | 12.1 | 33 | 9.2 | 24 | 23.5 | 33 | 22.5 | |||||||||
| September 2024 | 35 | 17.6 | 29 | 8.1 | 32 | 31.4 | 27 | 18.4 | 3 | 3.1 | 2 | 0.9 | |||||
| October 2024 | 26 | 13.1 | 44 | 12.2 | NA | NA | 26 | 26.8 | 44 | 20.7 | |||||||
| November 2024 | 30 | 15.1 | 50 | 13.9 | 30 | 30.9 | 50 | 23.5 | |||||||||
| December 2024 | 22 | 11.1 | 56 | 15.6 | 22 | 22.7 | 56 | 26.3 | |||||||||
| January 2025 | 7 | 3.5 | 38 | 10.6 | 7 | 7.2 | 38 | 17.8 | |||||||||
| February 2025 | 8 | 4.2 | 19 | 5.3 | 8 | 8.3 | 19 | 8.9 | |||||||||
| March 2025 | 1 | 0.5 | 4 | 1.1 | 1 | 1.0 | 4 | 1.9 | |||||||||
| Month of admission | |||||||||||||||||
| October 2024 | 3 | 1.1 | 3 | 0.8 | 3 | 2.9 | 2 | 1.4 | 0 | 0.0 | 1 | 0.5 | |||||
| November 2024 | 11 | 5.5 | 32 | 8.9 | 6 | 5.9 | 19 | 12.9 | 5 | 5.2 | 13 | 6.1 | |||||
| December 2024 | 58 | 29.2 | 64 | 17.8 | 34 | 33.3 | 25 | 17.0 | 24 | 24.7 | 39 | 18.3 | |||||
| January 2025 | 75 | 37.7 | 82 | 22.8 | 34 | 33.3 | 30 | 20.4 | 41 | 42.3 | 52 | 24.4 | |||||
| February 2025 | 35 | 17.6 | 77 | 21.4 | 18 | 17.7 | 33 | 22.5 | 17 | 17.5 | 44 | 20.7 | |||||
| March 2025 | 17 | 8.5 | 102 | 28.3 | 7 | 6.9 | 38 | 25.9 | 10 | 10.3 | 64 | 30.1 | |||||
| Age at admission | |||||||||||||||||
| 0–29 days | 27 | 13.6 | 61 | 16.9 | NA | NA | 27 | 27.8 | 61 | 28.6 | |||||||
| 30–59 days | 33 | 16.6 | 78 | 21.7 | 0 | 0 | 2 | 1.4 | 33 | 34.0 | 76 | 35.7 | |||||
| 60–89 days | 36 | 18.1 | 44 | 12.2 | 9 | 8.8 | 7 | 4.8 | 27 | 27.8 | 37 | 17.4 | |||||
| 90–119 days | 21 | 10.6 | 41 | 11.4 | 14 | 13.7 | 18 | 12.2 | 7 | 7.2 | 23 | 10.8 | |||||
| 120–149 days | 21 | 10.6 | 28 | 7.8 | 19 | 18.6 | 15 | 10.2 | 2 | 2.1 | 13 | 6.1 | |||||
| 150–179 days | 22 | 11.1 | 24 | 6.7 | 21 | 20.6 | 21 | 14.3 | 1 | 1.0 | 3 | 1.4 | |||||
| 180–209 days | 14 | 7.0 | 24 | 6.7 | 14 | 13.7 | 24 | 16.3 | NA | NA | |||||||
| 210–239 days | 11 | 5.5 | 21 | 5.8 | 11 | 10.8 | 21 | 14.3 | |||||||||
| ≥240 days | 14 | 7.0 | 39 | 10.8 | 14 | 13.7 | 39 | 26.5 | |||||||||
| Previous co-morbidities | |||||||||||||||||
| Malformations | 7 | 3.5 | 26 | 7.2 | 4 | 3.9 | 13 | 8.8 | 3 | 3.1 | 13 | 6.1 | |||||
| Cardiovascular disease* |
3 | 1.5 | 15 | 4.2 | 2 | 2.0 | 6 | 4.1 | 1 | 1.0 | 9 | 4.2 | |||||
| Respiratory disease* | 1 | 0.5 | 16 | 4.4 | 1 | 1.0 | 11 | 7.5 | 0 | 0.0 | 5 | 2.4 | |||||
| Liver disease* | 0 | 0.0 | 1 | 0.3 | 0 | 0.0 | 1 | 0.7 | 0 | 0.0 | 0 | 0.0 | |||||
| Kidney disease* | 1 | 0.5 | 0 | 0.0 | 1 | 1.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | |||||
| Immunodeficiencies | 2 | 1.0 | 3 | 0.8 | 1 | 1.0 | 1 | 0.7 | 1 | 1.0 | 2 | 0.9 | |||||
| Metabolic disorders | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | 0 | 0.0 | |||||
| Gestational age (weeks) | |||||||||||||||||
| ≥37 | 137 | 68.8 | 202 | 56.1 | 68 | 66.7 | 70 | 47.6 | 69 | 71.1 | 132 | 62.0 | |||||
| <37 | 10 | 5.0 | 52 | 14.4 | 5 | 4.9 | 24 | 16.3 | 5 | 5.2 | 28 | 13.2 | |||||
| Unknown | 52 | 26.1 | 106 | 29.4 | 29 | 28.4 | 53 | 36.1 | 23 | 23.7 | 53 | 24.9 | |||||
| Birth weight (g) | |||||||||||||||||
| ≥2,500 | 133 | 66.8 | 200 | 55.6 | 64 | 62.8 | 65 | 44.2 | 69 | 71.1 | 135 | 63.4 | |||||
| <2,500 | 10 | 5.0 | 52 | 14.4 | 6 | 5.9 | 28 | 19.1 | 4 | 4.1 | 24 | 11.3 | |||||
| Unknown | 56 | 28.1 | 108 | 30.0 | 32 | 31.4 | 54 | 36.7 | 24 | 24.7 | 54 | 25.4 | |||||
| RSV viral sub-group | |||||||||||||||||
| A | 46 | 23.1 | NA | 22 | 21.6 | 24 | 24.7 | NA | |||||||||
| B | 18 | 9.1 | 7 | 6.9 | NA | 11 | 11.3 | ||||||||||
| Unknown | 135 | 67.8 | 73 | 71.6 | 62 | 63.9 | |||||||||||
| Detection of SARS-CoV–2 or influenza | |||||||||||||||||
| SARS-CoV–2 | 2 | 1.0 | 8 | 2.3 | 1 | 1.0 | 5 | 3.5 | 1 | 1.0 | 3 | 1.4 | |||||
| Influenza | 4 | 2.0 | 29 | 8.1 | 2 | 2.0 | 16 | 10.9 | 2 | 2.1 | 13 | 6.1 | |||||
| No detection | 189 | 95.0 | 318 | 88.3 | 97 | 95.1 | 124 | 84.3 | 92 | 94.8 | 194 | 91.1 | |||||
| Unknown | 4 | 2.0 | 5 | 1.4 | 2 | 2.0 | 2 | 1.4 | 2 | 2.1 | 3 | 1.4 | |||||
| Nirsevimab administration | |||||||||||||||||
| No | 62 | 31.2 | 49 | 13.6 | 33 | 32.4 | 23 | 15.7 | 29 | 29.9 | 26 | 12.2 | |||||
| Yes | 137 | 68.8 | 311 | 86.4 | 69 | 67.7 | 124 | 84.4 | 68 | 70.1 | 187 | 87.8 | |||||
| Immunization month | |||||||||||||||||
| September | 19 | 13.9 | 34 | 10.9 | 18 | 26.1 | 33 | 26.6 | 1 | 1.5 | 1 | 0.5 | |||||
| October | 67 | 48.9 | 112 | 36.0 | 48 | 69.6 | 82 | 66.1 | 19 | 27.9 | 30 | 16.0 | |||||
| November | 27 | 19.7 | 57 | 18.3 | 2 | 2.9 | 5 | 4.0 | 25 | 36.8 | 52 | 27.8 | |||||
| December | 15 | 11.0 | 54 | 17.4 | 1 | 1.45 | 3 | 2.4 | 14 | 20.6 | 51 | 27.3 | |||||
| January | 4 | 2.9 | 30 | 9.7 | 0 | 0.0 | 1 | 0.8 | 4 | 5.9 | 29 | 15.5 | |||||
| February | 4 | 2.9 | 20 | 6.4 | 0 | 0.0 | 0 | 0.0 | 4 | 5.9 | 20 | 10.7 | |||||
| March | 1 | 0.7 | 4 | 1.3 | 0 | 0.0 | 0 | 0.0 | 1 | 1.5 | 4 | 2.1 | |||||
| Time since immunization | |||||||||||||||||
| 0–34 days | 27 | 19.7 | 98 | 31.5 | 3 | 4.4 | 14 | 11.3 | 24 | 35.3 | 84 | 44.9 | |||||
| 35–69 days | 41 | 29.9 | 78 | 25.1 | 12 | 17.4 | 21 | 16.9 | 29 | 42.6 | 57 | 30.5 | |||||
| ≥ 70 days | 69 | 50.4 | 135 | 43.4 | 54 | 78.3 | 89 | 71.8 | 15 | 22.1 | 46 | 24.6 | |||||
| Median time (days) since immunization (IQR) | 70 (40–101) |
56 (30–104) |
94 (71–116) |
99.5 (58–140) |
43 (29–66.5) |
40 (20–68) |
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| Infection severity | |||||||||||||||||
| ICU admission | 52 | 26.1 | 61 | 16.9 | 15 | 14.7 | 19 | 13.0 | 37 | 38.1 | 42 | 19.7 | |||||
| Deceased | 0 | 0.0 | 1 | 0.3 | 0 | 0.0 | 1 | 0.7 | 0 | 0.0 | 0 | 0.0 | |||||
ICU, intensive care unit; IQR, interquartile range; NA, not applicable; RSV, respiratory syncytial virus.
*
As chronic condition.