Primary prevention
Vaccines
Until 2022 there was no vaccine available against respiratory syncytial virus (RSV). Difficulties encountered in RSV vaccine development include: ineffective protective immunity arising from natural infection; difficulty establishing end point metrics for measuring vaccine response; and the need for rigorous safety analysis due to enhanced disease severity caused by a formalin-inactivated RSV vaccine candidate in the 1960s.[57]
In 2023, the first two vaccines for the prevention of RSV were approved by the Food and Drug Administration (FDA) and European Medicines Agency (EMA). The first vaccine (commercially known as Arexvy®) is a recombinant RSV-specific antigen glycoprotein F stabilized in the prefusion conformation (RSVPreF3), combined with the AS01E adjuvant system. The second vaccine (commercially known as Abrysvo®) is a bivalent RSV prefusion F (RSVpreF) protein-based vaccine.
Both Abrysvo® and Arexvy® are approved for the active immunization of adults ages ≥60 years for the prevention of lower respiratory tract disease caused by RSV. Arexvy® is also approved by the FDA and EMA for the prevention of RSV lower respiratory tract disease in adults ages 50-59 years who are at increased risk.
Abrysvo® is recommended for use in pregnant women between 32 and 36 weeks' gestation using seasonal administration (i.e., during September through the end of January in most of the continental US) to provide passive protection against lower respiratory tract disease caused by RSV in infants from birth through to 6 months of age.[58][59]
In large, randomized, controlled trials in adults ages ≥60 years, the vaccines provided up to 70% efficacy in preventing RSV infection and up to 90% efficacy against severe disease, when dosed intramuscularly once prior to RSV season, with good safety profiles.[60][61] Further data about the possible need for annual repeat dosing are not yet available.
When pregnant women between 24 and 36 weeks' gestation were administered one dose of RSVpreF, the efficacy for prevention of RSV infection in their infants up to 6 months of age was 50%, and for prevention of severe RSV disease in infants up to 6 months of age was almost 70% compared to infants of mothers who received the placebo. Somewhat higher rates of protection against both infection and severe disease were seen in the first 3 months of life in the infants of vaccinated mothers.[62] A 2024 systematic review including six RCTs (25 study reports) comparing RSV vaccination with placebo in 17,991 pregnant women concluded that RSV vaccination during pregnancy reduces RSV‐related hospitalizations in infants and has little or no effect on the risk of birth defects.[63]
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In 2024, the FDA and EMA also approved an mRNA vaccine (commercially known as Mresvia®) to protect adults ages ≥60 years from lower respiratory tract disease caused by RSV infection. The vaccine contains an mRNA sequence that encodes RSV glycoprotein F stabilized in the prefusion conformation. This glycoprotein, crucial for viral entry into host cells, is expressed on the surface of the virus. The prefusion conformation of the F protein is a significant target of potent neutralizing antibodies and is highly conserved across both RSV-A and RSV-B subtypes.
Data from the phase 3 ConquerRSV clinical trial, involving 35,541 adults ages ≥60 years in 22 countries, showed a vaccine efficacy for the mRNA vaccine of 83.7% against RSV-associated lower respiratory tract disease with at least two signs or symptoms and 82.4% against the disease with at least three signs or symptoms over a median follow-up of 3.7 months.[64]
Immunoprophylaxis
Palivizumab and nirsevimab are monoclonal antibodies that are directed at targets on the RSV F protein and are approved for RSV immunoprophylaxis in infants and children. Nirsevimab is a monoclonal antibody engineered to bind to the prefusion RSV F protein and with an Fc region engineered to prolong its half-life. The changes improve the drug’s efficacy (with early studies showing that the risk of hospitalization for RSV is decreased by up to 80% as compared to about a 50% decrease in risk of hospitalization with palivizumab use) and give it the advantage of only requiring a single intramuscular dose (compared to 5 doses with palivizumab).[65][66]
Palivizumab
Palivizumab was the first monoclonal antibody indicated for the prevention of serious lower respiratory tract disease caused by RSV in high-risk infants and children. It is still approved in the US and Europe.
Immunoprophylaxis with palivizumab for infants at high risk reduced hospital admissions by 45% to 55% and was associated with a reduction in all-cause mortality.[67][68] The need for frequent injections and its expense limited its use on a large scale.[69]
Current indications for use of palivizumab are based on shortages of nirsevimab. There is no known indication for using palivizumab when nirsevimab is available, given the lower cost, easier administration, and likely greater efficacy of nirsevimab. Neither palivizumab nor nirsevimab is indicated for treating active RSV infection.[70]
Nirsevimab
Nirsevimab is a long-acting RSV F protein-directed fusion inhibitor monoclonal antibody indicated for the prevention of RSV lower respiratory tract disease in pediatric patients. It is approved in the US and Europe. In the US, it is approved for children up to the age of 19 months. In Europe, it is approved for children up to the age of 24 months. Nirsevimab has an extended half-life, and is intended to protect infants for an entire RSV season with a single intramuscular dose.[71]
The American Academy of Pediatrics (AAP) recommends that all infants, especially those at high risk, receive a single dose of nirsevimab. Specifically the AAP and the Center for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) recommend a single dose of nirsevimab for:[72][73][74]
All infants <8 months of age born during or entering their first RSV season
Infants and children 8-19 months of age who are at increased risk of severe disease and entering their second RSV season
These recommendations were amended for the 2022-2023 season due to supply chain issues, but remain the ACIP recommendations when the needed supply of nirsevimab is available.
In healthy preterm infants, nirsevimab resulted in fewer hospitalizations for RSV-associated lower respiratory tract infections compared with placebo.[65] One phase 3 trial found that a single dose of nirsevimab provided protection against medically attended RSV-associated lower respiratory tract infection when given to healthy late-preterm and term infants before an RSV season.[66] The safety and efficacy of nirsevimab were supported by three clinical trials which found that nirsevimab reduced the risk of RSV lower respiratory tract infection by approximately 70% to 75% relative to placebo.[66][75][76][77] Initial results of a population-based longitudinal study conducted in Spain show that nirsevimab substantially reduced infant hospitalizations for RSV-associated LRTI, severe RSV-associated LRTI requiring oxygen, and all-cause LRTI when given in real-world conditions.[78]
Secondary prevention
Hand washing in the clinical and nonclinical settings is important.[2] Hand washing and washing of shared toys is important for all family members and close contacts to limit spread of respiratory syncytial virus (RSV) infection.
Patients requiring hospitalization should be placed in isolation with contact precautions.[8] Proper use of barriers such as gowns, gloves, and masks is effective if large respiratory droplets are present and should be worn when providing care to these patients.[156][157][158][159] An N95 respiratory mask is not required, and is not more effective than a simple surgical mask.[34][89][160] Screening for RSV in suspected patients allows for cohorting and isolation of patients with confirmed infection, limiting further spread of the virus.[89]
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