Table 3.
Effectiveness of catch-up and at-birth nirsevimab immunization against hospitalization for respiratory syncytial virus infection in the first year of life, Spain, 2024/2025 season (based on data from n = 559 children)
| Cases | Controls | Crude IE (95% CI) | Adjusted IE** (95% CI) | |||
|---|---|---|---|---|---|---|
| Immunized | Total | Immunized | Total | |||
| Catch-up immunization | ||||||
| Overall | 69 | 102 | 124 | 147 | 58.8 (21.3 to 78.5) | 63.6 (26.9 to 81.9) |
| Time since immunization | ||||||
| 0–34 days | 3 | 37* | 14 | 37* | NA | NA |
| 35–69 days | 12 | 46* | 21 | 44* | 74.0 (30.9 to 90.2) | 80.0 (42.2 to 93.1) |
| ≥70 days | 54 | 88* | 89 | 112* | 47.0 (–6.7 to 73.7) | 53.6 (1.7 to 78.1) |
| Age at admission | ||||||
| <60 days | 0 | 0 | 2 | 2 | NA | NA |
| 60–119 days | 16 | 23 | 23 | 25 | 83.3 (3.8 to 97.1) | 81.1 (–27.7 to 97.2) |
| 120–179 days | 28 | 40 | 33 | 36 | 77.2 (8.3 to 94.3) | 74.8 (–4.8 to 93.9) |
| ≥180 days | 25 | 39 | 66 | 84 | 38.2 (–51.0 to 74.7) | 43.9 (–43.2 to 78.0) |
| At-birth immunization | ||||||
| Overall | 68 | 97 | 187 | 213 | 68.4 (40.6 to 83.2) | 70.4 (43.4 to 84.5) |
| Time since immunization | ||||||
| 0–34 days | 24 | 53* | 84 | 111* | 77.6 (52.4 to 89.5) | 82.2 (57.1 to 92.6) |
| 35–69 days | 29 | 58* | 57 | 84* | 62.4 (21.7 to 82.0) | 65.8 (22.9 to 84.8) |
| ≥70 days | 15 | 44* | 46 | 73* | 58.3 (3.3 to 82.1) | 35.2 (–105 to 79.6) |
| Age at admission | ||||||
| 0–29 days | 16 | 27 | 54 | 61 | 81.7 (41.0 to 94.3) | 89.2 (59.0 to 97.2) |
| 30–59 days | 22 | 33 | 67 | 76 | 76.3 (31.9 to 91.7) | 80.3 (41.1 to 93.4) |
| 60–89 days | 21 | 27 | 32 | 37 | 61.0 (–61.2 to 90.5) | 51.9 (–106 to 88.8) |
| ≥90 days | 9 | 10 | 34 | 39 | NA | NA |
CI, confidence intervals; NA, not applicable; IE, immunization effectiveness.
The number of total cases and controls in time since immunization intervals include the total number of non-immunized infants plus the number in each time since immunization interval, respectively, for cases and controls.
Logistic regression, adjusted by sex, risk factors, week of admission (NCS with two inner knots), age at admission (NCS with two inner knots), and RSV hospitalization rate (per 100000 population, by region and epidemiological week) (NCS with two inner knots). All models are based on between 5 and 10 cases per variable.