Efficacy and safety of respiratory syncytial virus vaccines.

Rationale: Respiratory syncytial virus (RSV) is a highly transmissible pathogen that causes varying degrees of respiratory illness across all age groups. The safety and efficacy profiles of available RSV vaccines, a critical consideration for their integration into public health strategies and clinical practice, remain uncertain.

Objectives: To assess the benefits and harms of RSV vaccines compared to placebo, no intervention, vaccines for other respiratory infections, other RSV vaccines, or monoclonal antibodies (mAbs) across all human populations.

Search methods: We conducted a comprehensive literature search of CENTRAL, MEDLINE, Embase, ClinicalTrials.gov, and the WHO ICTRP following standard systematic review methodology from 2000 to April 2024.

Eligibility criteria: We included both randomised controlled trials (RCTs) and non-randomised studies of interventions (NRSIs) involving all human populations comparing RSV vaccines with placebo, no intervention, vaccines for other respiratory infections, other RSV vaccines, or mAbs. We excluded studies focused on dose-finding schedules and immunogenicity assessment.

Outcomes: Benefits included frequency of RSV illness (both lower and upper respiratory illness) confirmed by laboratory tests (RSV-associated lower respiratory tract illness and RSV-associated acute respiratory illness); hospitalisation due to RSV disease (both lower and upper respiratory illness) confirmed by laboratory tests; mortality from illness caused by RSV (confirmed by laboratory test); all-cause mortality; and admission to an intensive care unit. Harms included serious adverse events (SAEs) related to vaccination, including neurological disorders such as Guillain-Barré syndrome.

Risk of bias: We assessed risk of bias in RCTs using Cochrane's RoB 2 tool.

Synthesis methods: We used standard Cochrane methods.

Included studies: We identified 14 RCTs: five trials (101,825 participants) on older adults; three trials (12,010 participants) on maternal vaccination and effects on infants; one trial (300 participants) on women of childbearing age; and five trials (192 participants) on infants and children. We identified no NRSIs.

Synthesis of results: RSV prefusion vaccine versus placebo in older adults These vaccines reduced RSV-associated lower respiratory tract illness with vaccine efficacy (VE) of 77% (95% confidence interval (CI) 0.70 to 0.83; risk ratio (RR) 0.23, 95% CI 0.17 to 0.30; 4 RCTs, 99,931 participants; high-certainty evidence) and RSV-associated acute respiratory illness with VE of 67% (95% CI 0.60 to 0.73; RR 0.33, 95% CI 0.27 to 0.40; 3 RCTs, 94,339 participants; high-certainty evidence). There may be little to no difference in mortality from illness caused by RSV, all-cause mortality, and SAEs related to vaccination (low-certainty evidence). RSV postfusion F protein-based vaccine versus placebo in older adults There is probably little to no difference in RSV-associated lower respiratory tract illness with VE of -0.37% (95% CI -1.96 to 0.37; RR 1.37, 95% CI 0.63 to 2.96; 1 RCT, 1894 participants; moderate-certainty evidence) and RSV-associated acute respiratory illness with VE of -0.07% (95% CI -1.15 to 0.47; RR 1.07, 95% CI 0.53 to 2.15; 1 RCT, 1894 participants; moderate-certainty evidence). There may be little to no difference in mortality from illness caused by RSV, all-cause mortality, and SAEs related to vaccination (low-certainty evidence). Maternal RSV F protein-based vaccine versus placebo in infants These vaccines reduced medically attended RSV-associated lower respiratory tract illness with VE of 54% (95% CI 0.28 to 0.71; RR 0.46, 95% CI 0.29 to 0.72; 3 RCTs, 12,010 participants; high-certainty evidence), medically attended RSV-associated severe lower respiratory tract illness with VE of 74% (95% CI 0.44 to 0.88; RR 0.26, 95% CI 0.12 to 0.56; 3 RCTs, 12,010 participants; high-certainty evidence), and hospitalisation due to RSV disease with VE of 54% (95% CI 0.27 to 0.71; RR 0.46, 95% CI 0.29 to 0.73; 2 RCTs, 11,502 participants; high-certainty evidence) in infants. There may be little to no difference in mortality from illness caused by RSV, all-cause mortality, and SAEs related to vaccination in mothers and infants (low-certainty evidence). Live-attenuated RSV vaccines versus placebo in infants and children The evidence is very uncertain regarding all-cause medically attended acute respiratory illness (MAARI) with VE of 26% (95% CI -0.01 to 0.46; RR 0.74, 95% CI 0.54 to 1.01; 5 RCTs, 171 participants; very low-certainty evidence) and RSV-associated MAARI with VE of 38% (95% CI -0.24 to 0.69; RR 0.62, 95% CI 0.31 to 1.24; 5 RCTs, 192 participants; very low-certainty evidence). There may be little to no difference in SAEs related to vaccination (low-certainty evidence). RSV recombinant F nanoparticle vaccine versus placebo in women of childbearing age The evidence is very uncertain regarding new RSV infections with VE of 50% (95% CI 0.08 to 0.73; RR 0.50, 95% CI 0.27 to 0.92; 1 RCT, 300 participants; very low-certainty evidence). There may be little to no difference in mortality from illness caused by RSV, all-cause mortality, and SAEs related to vaccination (low-certainty evidence). Phase III trials consistently demonstrated low risk of bias. Whilst phase I and II trials occasionally raised concerns about selection bias in the randomisation process, the overall evidence was deemed robust.

Authors' conclusions: RSV prefusion vaccines reduced RSV-associated lower respiratory tract illness and acute respiratory illness in older adults. There may be little to no difference in SAEs related to vaccination in older adults. Maternal vaccination with RSV F protein-based vaccines reduced medically attended RSV-associated lower respiratory tract illness and severe cases in infants. There may be little to no difference in SAEs related to vaccination in mothers and infants. The evidence is very uncertain regarding the effects of RSV vaccine on women of childbearing age, and the effects of live-attenuated RSV vaccines on infants and children; there may be little to no difference in SAEs related to vaccination.

Funding: This review was funded by the EU4Health Programme under a service contract with the European Health and Digital Executive Agency (HaDEA).

Registration: The review was registered in the International Prospective Register of Systematic Reviews (PROSPERO) (CRD42023439128).