Preventing respiratory syncytial virus in infants

Clinical question

How safe and effective are monoclonal antibodies in preventing respiratory syncytial virus (RSV) in infants?

Bottom line

In infants at high risk (born prematurely or with congenital heart or lung conditions), palivizumab (4 to 5 monthly doses during RSV season) reduces RSV hospitalization (4.4% vs 9.8% placebo). Nirsevimab (1 dose) reduces RSV hospitalizations in healthy premature infants (0.8% vs 4.1%) and term infants (0.3%-0.4% vs 1.5%-2.0%). Side effects are similar to placebo.

Evidence

Comparisons are statistically different unless indicated.

• Palivizumab is given as 4 to 5 monthly doses during RSV season. A systematic review (5 RCTs, 3443 infants)¹ with 2 dominant placebo-controlled RCTs included infants born at 35 weeks or less or with bronchopulmonary dysplasia² or congenital heart disease.³ At 2 years, hospitalization rates due to RSV were 4.4% versus 9.8% (placebo), with a relative risk reduction (RRR)=55% and number needed to vaccinate (NNV)=19. Mortality rates (1.3% vs 2.3% [placebo]) were not statistically different.

• Nirsevimab given as a single dose before or during RSV season was compared with placebo.^4-6

  • - In 1453 healthy premature infants (born between 29 and 35 weeks’ gestation),⁴ rates of hospitalization due to RSV at 150 days after dose administration were 0.8% versus 4.1% (placebo), with RRR=81% and NNV=31. Mortality rates after 1 year were 0.2% versus 0.6% (placebo), not statistically different (authors’ calculation).

  • - In term or near-term healthy infants (N=3012),^5,6 RSV hospitalization rates at 150 days were 0.4% versus 2.0% (placebo),⁶ with RRR=78% and NNV=63.

• Nirsevimab was also compared with no treatment (unblinded).⁷ Among 8058 infants (85.2% born at ≥37 weeks), RSV hospitalization rates at 3 months were 0.3% versus 1.5% (no treatment), with RRR=82% and NNV=82.

• Adverse events were similar between palivizumab, nirsevimab, and placebo.^1,4-8

• Limitations: Many RCT authors were shareholders or employees of the industry funder.^4,5

Context

• In Canada RSV is responsible for about 2600 childhood hospitalizations annually.⁹ Among those hospitalized aged 2 years or younger,¹⁰ close to 80% have no underlying medical conditions and the mortality rate is 0.2%.

• In the northern hemisphere most RSV infections occur between November and April.¹¹

Implementation

The National Advisory Committee on Immunization recommends nirsevimab for several infant groups, including those at increased risk of severe RSV disease during their first season (eg, born at <37 weeks’ gestation or with chronic lung or heart disease).¹¹ Nirsevimab is also recommended for infants at higher risk in their second RSV season and those living in remote Indigenous communities. The National Advisory Committee on Immunization also recommends that nirsevimab be considered for any infant younger than 8 months entering their first RSV season if cost effective. Nirsevimab is anticipated to be less costly (per vaccine) and preferred over palivizumab.¹²