After a nationwide nirsevimab rollout, infant ear infections fell 44%

Respiratory syncytial virus is the leading cause of lower-respiratory infection in babies, and it has a knock-on effect that gets less attention than the wheezing and hospital admissions: ear infection. Acute otitis media is among the most frequent complications of RSV in infancy, and it is the leading reason antibiotics are prescribed to this age group [s1].

Nirsevimab, a long-acting monoclonal antibody given as a single injection, was shown in the MELODY trial to prevent medically attended RSV lower-respiratory infection in healthy late-preterm and term infants, and it has since been rolled out as a seasonal programme in several countries [s2][s1]. A study published in the European Journal of Pediatrics on 9 October asks a downstream question: once such a programme is in place, do ear infections fall too? [s1]

What was measured

The researchers ran a nationwide, register-based interrupted time-series analysis — a design that looks for a break in a trend at the point an intervention is introduced. They drew on national data covering live births, laboratory-confirmed RSV detections, and acute otitis media diagnoses across four consecutive RSV seasons, from 2022–2023 through 2025–2026 [s1].

Because RSV is seasonal, the analysis focused on the peak months of December to March. Monthly infant populations at risk were reconstructed from birth cohorts, and incidence rates during two RSV seasons before the nirsevimab programme were compared with the two seasons after it, in infants under 12 months, split into age bands of 0–2, 3–5, and 6–11 months [s1].

The scale is what gives the study its weight. The population comprised 181,999 infants, with 2,022,261 infant-months of follow-up. The primary analysis included 3,699 RSV-positive findings and 15,830 acute otitis media diagnoses [s1].

The result

Following nirsevimab implementation, the incidence of acute otitis media among infants under 12 months fell by 44% (rate ratio 0.56, 95% confidence interval 0.54 to 0.58) [s1]. RSV detections over the same period fell by 83% (rate ratio 0.17, 95% CI 0.15 to 0.18) [s1].

The reduction in ear infections was greatest in the youngest babies, those aged 0–2 months [s1]. That pattern is what you would expect if the effect is real and mediated by RSV: the youngest infants are both the most vulnerable to severe RSV and the group a birth-dose immunisation programme reaches first.

The authors conclude that implementing a nirsevimab immunisation programme was associated with a substantial reduction in acute otitis media, suggesting RSV immunisation may lower the burden of ear infection in early childhood [s1].

What the design can and cannot show

An interrupted time-series is one of the stronger observational designs, because each population acts partly as its own control and the question is whether the trend shifts when the intervention arrives. But it is still observational, and it cannot by itself rule out other things that changed between the pre- and post-seasons.

The most important confounder is other RSV-season dynamics. RSV activity varies year to year, and the 2022–2023 seasons were still shaped by shifting post-pandemic circulation. A quieter RSV season after rollout would lower both RSV detections and RSV-driven ear infections regardless of nirsevimab. The parallel 83% drop in RSV itself is consistent with a real antibody effect, but the study design means the ear-infection fall is an association, not a demonstrated causal reduction in every child.

The study also counts diagnoses, not every true infection, and diagnostic and prescribing habits can drift over four years.

Why it matters

Ear infections are not merely uncomfortable; they drive a large share of early-childhood antibiotic use, and antibiotic exposure in infancy is something public-health systems are trying to reduce. If a seasonal RSV antibody programme reliably cuts ear infections as well as severe chest disease, the case for it broadens from preventing hospital admissions to easing a common, antibiotic-heavy complication of infancy [s1]. This study is early real-world evidence for that broader benefit, and a reason to watch whether the same pattern appears as more countries report their own rollouts.

This article is informational and does not constitute medical advice.