Incidence Rates of Lower Respiratory Infection–Associated Hospitalizations by Study Group
| Outcome and Infant Age . | IIV . | Placebo . | Incidence Rate Ratio (95% CI) . | P Value . | Adjusted Incidence Rate Ratiob (95% CI) . | Adjusted P Valueb . | ||
|---|---|---|---|---|---|---|---|---|
| No. . | Rate (95% CI)a . | No. . | Rate (95% CI)a . | |||||
| Overall study follow-up | ||||||||
| Infants ≤90 d | 9 | 3.0 (1.6–5.9) | 21 | 7.2 (4.7–11.0) | 0.43 (.19–.93) | .032 | 0.42 (.19–.92) | .030 |
| Infants 91–175 d | 10 | 3.8 (2.0–7.1) | 12 | 4.6 (2.6–8.1) | 0.83 (.36–1.9) | .66 | 0.82 (.36–1.9) | .65 |
| Infants ≤175 d | 19 | 3.4 (2.2–5.4) | 33 | 6.0 (4.3–8.5) | 0.57 (.32–1.0) | .050 | 0.56 (.32–.99) | .046 |
| During extended influenza seasonc | ||||||||
| Infants ≤90 d | 8 | 3.4 (1.7–6.9) | 15 | 6.3 (3.8–10.4) | 0.55 (.23–1.3) | .17 | 0.54 (.23–1.3) | .16 |
| Infants 91–175 d | 6 | 6.7 (3.0–14.9) | 6 | 6.9 (3.1–15.4) | 0.97 (.31–3.0) | .95 | 0.98 (.32–3.0) | .97 |
| Infants ≤175 d | 14 | 4.4 (2.6–7.4) | 21 | 6.5 (4.2–10.0) | 0.67 (.34–1.3) | .25 | 0.67 (.34–1.3) | .24 |
| Outside extended influenza season | ||||||||
| Infants ≤175 d | 5 | 2.1 (.88–5.1) | 12 | 5.2 (3.0–9.2) | 0.40 (.14–1.1) | .09 | 0.40 (.14–1.1) | .09 |
| Outcome and Infant Age . | IIV . | Placebo . | Incidence Rate Ratio (95% CI) . | P Value . | Adjusted Incidence Rate Ratiob (95% CI) . | Adjusted P Valueb . | ||
|---|---|---|---|---|---|---|---|---|
| No. . | Rate (95% CI)a . | No. . | Rate (95% CI)a . | |||||
| Overall study follow-up | ||||||||
| Infants ≤90 d | 9 | 3.0 (1.6–5.9) | 21 | 7.2 (4.7–11.0) | 0.43 (.19–.93) | .032 | 0.42 (.19–.92) | .030 |
| Infants 91–175 d | 10 | 3.8 (2.0–7.1) | 12 | 4.6 (2.6–8.1) | 0.83 (.36–1.9) | .66 | 0.82 (.36–1.9) | .65 |
| Infants ≤175 d | 19 | 3.4 (2.2–5.4) | 33 | 6.0 (4.3–8.5) | 0.57 (.32–1.0) | .050 | 0.56 (.32–.99) | .046 |
| During extended influenza seasonc | ||||||||
| Infants ≤90 d | 8 | 3.4 (1.7–6.9) | 15 | 6.3 (3.8–10.4) | 0.55 (.23–1.3) | .17 | 0.54 (.23–1.3) | .16 |
| Infants 91–175 d | 6 | 6.7 (3.0–14.9) | 6 | 6.9 (3.1–15.4) | 0.97 (.31–3.0) | .95 | 0.98 (.32–3.0) | .97 |
| Infants ≤175 d | 14 | 4.4 (2.6–7.4) | 21 | 6.5 (4.2–10.0) | 0.67 (.34–1.3) | .25 | 0.67 (.34–1.3) | .24 |
| Outside extended influenza season | ||||||||
| Infants ≤175 d | 5 | 2.1 (.88–5.1) | 12 | 5.2 (3.0–9.2) | 0.40 (.14–1.1) | .09 | 0.40 (.14–1.1) | .09 |
Abbreviations: CI, confidence interval; IIV, inactivated influenza vaccine.
aRates calculated as number of cases per 1000 infant-months, using person time between birth and event or end of study.
bAdjusted for birth weight <2500 g and sex.
cExtended influenza season was defined as the period between 2 weeks prior to the start of and 2 weeks after end of the epidemic influenza period each year.
Incidence Rates of Lower Respiratory Infection–Associated Hospitalizations by Study Group
| Outcome and Infant Age . | IIV . | Placebo . | Incidence Rate Ratio (95% CI) . | P Value . | Adjusted Incidence Rate Ratiob (95% CI) . | Adjusted P Valueb . | ||
|---|---|---|---|---|---|---|---|---|
| No. . | Rate (95% CI)a . | No. . | Rate (95% CI)a . | |||||
| Overall study follow-up | ||||||||
| Infants ≤90 d | 9 | 3.0 (1.6–5.9) | 21 | 7.2 (4.7–11.0) | 0.43 (.19–.93) | .032 | 0.42 (.19–.92) | .030 |
| Infants 91–175 d | 10 | 3.8 (2.0–7.1) | 12 | 4.6 (2.6–8.1) | 0.83 (.36–1.9) | .66 | 0.82 (.36–1.9) | .65 |
| Infants ≤175 d | 19 | 3.4 (2.2–5.4) | 33 | 6.0 (4.3–8.5) | 0.57 (.32–1.0) | .050 | 0.56 (.32–.99) | .046 |
| During extended influenza seasonc | ||||||||
| Infants ≤90 d | 8 | 3.4 (1.7–6.9) | 15 | 6.3 (3.8–10.4) | 0.55 (.23–1.3) | .17 | 0.54 (.23–1.3) | .16 |
| Infants 91–175 d | 6 | 6.7 (3.0–14.9) | 6 | 6.9 (3.1–15.4) | 0.97 (.31–3.0) | .95 | 0.98 (.32–3.0) | .97 |
| Infants ≤175 d | 14 | 4.4 (2.6–7.4) | 21 | 6.5 (4.2–10.0) | 0.67 (.34–1.3) | .25 | 0.67 (.34–1.3) | .24 |
| Outside extended influenza season | ||||||||
| Infants ≤175 d | 5 | 2.1 (.88–5.1) | 12 | 5.2 (3.0–9.2) | 0.40 (.14–1.1) | .09 | 0.40 (.14–1.1) | .09 |
| Outcome and Infant Age . | IIV . | Placebo . | Incidence Rate Ratio (95% CI) . | P Value . | Adjusted Incidence Rate Ratiob (95% CI) . | Adjusted P Valueb . | ||
|---|---|---|---|---|---|---|---|---|
| No. . | Rate (95% CI)a . | No. . | Rate (95% CI)a . | |||||
| Overall study follow-up | ||||||||
| Infants ≤90 d | 9 | 3.0 (1.6–5.9) | 21 | 7.2 (4.7–11.0) | 0.43 (.19–.93) | .032 | 0.42 (.19–.92) | .030 |
| Infants 91–175 d | 10 | 3.8 (2.0–7.1) | 12 | 4.6 (2.6–8.1) | 0.83 (.36–1.9) | .66 | 0.82 (.36–1.9) | .65 |
| Infants ≤175 d | 19 | 3.4 (2.2–5.4) | 33 | 6.0 (4.3–8.5) | 0.57 (.32–1.0) | .050 | 0.56 (.32–.99) | .046 |
| During extended influenza seasonc | ||||||||
| Infants ≤90 d | 8 | 3.4 (1.7–6.9) | 15 | 6.3 (3.8–10.4) | 0.55 (.23–1.3) | .17 | 0.54 (.23–1.3) | .16 |
| Infants 91–175 d | 6 | 6.7 (3.0–14.9) | 6 | 6.9 (3.1–15.4) | 0.97 (.31–3.0) | .95 | 0.98 (.32–3.0) | .97 |
| Infants ≤175 d | 14 | 4.4 (2.6–7.4) | 21 | 6.5 (4.2–10.0) | 0.67 (.34–1.3) | .25 | 0.67 (.34–1.3) | .24 |
| Outside extended influenza season | ||||||||
| Infants ≤175 d | 5 | 2.1 (.88–5.1) | 12 | 5.2 (3.0–9.2) | 0.40 (.14–1.1) | .09 | 0.40 (.14–1.1) | .09 |
Abbreviations: CI, confidence interval; IIV, inactivated influenza vaccine.
aRates calculated as number of cases per 1000 infant-months, using person time between birth and event or end of study.
bAdjusted for birth weight <2500 g and sex.
cExtended influenza season was defined as the period between 2 weeks prior to the start of and 2 weeks after end of the epidemic influenza period each year.
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