- Design
- Phase 3, randomised, partially masked, palivizumab-controlled trial
- Population
- 997 palivizumab-eligible infants at high risk of severe RSV
- Primary outcome
- Adverse events in season 1
- Effect
- AEs comparable; RSV MALRI 3.2% vs 3.4% through day 150
SMART was a phase 3, partially masked trial at 110 sites in 27 countries. It randomised 997 palivizumab-eligible infants — premature, with chronic lung disease of prematurity or with haemodynamically significant congenital heart disease — to a single 105 mg dose of clesrovimab, a long-acting monoclonal antibody, or up to five monthly doses of palivizumab. Eligible children received open-label clesrovimab 210 mg before their second season.
Adverse events in season 1 were comparable. RSV-associated medically attended lower respiratory infection through day 150 was 3.2% with clesrovimab and 3.4% with palivizumab. In season 2, the 210 mg dose was well tolerated, and RSV lower respiratory infection through day 180 was 7.3%.
The primary outcome was safety, not efficacy, and the trial was not designed to show superiority. What it does show is that one injection can replace five in the infants who most need protection, which matters for adherence and clinic workload. Clesrovimab's availability and price in India are not established.
- For high-risk infants, a single long-acting RSV antibody dose can replace monthly palivizumab where available.
- Children still at risk in their second season — chronic lung disease, significant heart disease — can receive a second-season dose.
- Give the dose before or at the start of the local RSV season.
- Check availability locally; palivizumab remains an option where long-acting antibodies are not supplied.
Why it matters
It removes the monthly injection burden for the infants at highest risk of severe RSV.
Don't overread it
The primary end point was safety; efficacy comparisons are secondary and the second season was uncontrolled.
The statistics, in plain English
The RSV infection rates (3.2% vs 3.4%) have overlapping confidence intervals, so the two products performed similarly, but the trial was powered for safety, not to prove equal efficacy. The second-season figure comes from an open-label, single-arm phase with no comparator.
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