Maternal RSVpreF Vaccine Effectiveness Against Respiratory Syncytial Virus in Hospitalized Infants

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"Results Of 1012 infants hospitalized with ARI, 655 had LRTD, with 114 of 386 case infants (30%) and 171 of 269 control infants (64%) born to RSVpreF-vaccinated mothers (median [IQR] gestational age at vaccination, 31 weeks [29-33]). Median (IQR) maternal age at delivery was 32 years (29-35). Median (IQR) age of infants hospitalized for LRTD was 52 days (30-89); 495 of 655 (76%) were aged 3 months or younger. VE against RSV-LRTD hospitalization was 77.8% (95% CI, 66.4%-85.3%) among infants from birth through 6 months of age, 80.2% (95% CI, 71.1%-86.5%) among infants from birth through 3 months of age, 86.3% (95% CI, 79.0%-91.1%) among infants from birth through 2 months of age, and 68.2% (95% CI, 42.2%-82.5%) among infants older than 2 months through 4 months of age. Comparable VE among infants aged 6 months or younger was observed for severe RSV-LRTD (80.4%; 95% CI, 54.4%-91.6%) and RSV-ARI (80.8%; 95% CI, 70.4%-87.6%) hospitalization, with similar age-specific trends. VE was consistent across stratifications by gestational age at vaccination, vaccination to delivery time interval, and proximal administration with other vaccines during pregnancy. Descriptively, among all infants hospitalized with ARI, 161 of 499 (32%) born to RSVpreF-unvaccinated mothers had severe LRTD, while 87 of 513 (17%) born to RSVpreF-vaccinated mothers had severe LRTD.

Conclusions and Relevance Findings in this case-control study demonstrate high year-round effectiveness of RSVpreF vaccination against RSV-associated hospitalization in infants 6 months of age or younger in the first year following introduction in Australia, with the highest VE observed in the earliest age intervals. Future analyses with larger sample sizes will evaluate VE among additional subgroups."