What information is available on vaccines for the prevention of RSV?

Background
Respiratory syncytial virus (RSV) is a single-stranded RNA virus that causes significant respiratory disease in children, the elderly, and other high-risk patient groups.1 Outbreaks of RSV occur annually; RSV season typically begins in the fall and peaks in the winter.2 The virus is transmitted from person to person through saliva and mucus droplets. Symptoms begin 3 to 7 days after infection and may include fever, runny or stuffy nose, cough, chest tightness, wheezing, and dyspnea. Nearly all children are infected with RSV in the first 2 years of life, and while some degree of immunity is usually achieved, reinfections occur often in both children and adults.3 While many cases of RSV are mild and result in few or no symptoms, RSV can lead to serious respiratory illness requiring hospitalization, mechanical ventilation, or even death in some patients.2

Severe RSV is a leading cause of infant hospitalization globally; in the United States, it is estimated that 58,000 to 80,000 RSV-associated hospitalizations and 100 to 300 RSV-associated deaths occur each year in children aged <5 years.1,4 Severe disease is most common in very young infants and infants with other underlying conditions.2 Premature infants and infants aged ≤6 months are at increased risk of severe disease, as are children aged <2 years with chronic lung disease or congenital heart disease. Additional at-risk pediatric populations include children with suppressed or weakened immune systems, children with neuromuscular disorders or a congenital anomaly, and children with severe cystic fibrosis.

Certain adult populations are also significantly impacted by RSV.3 It has been estimated that RSV leads to 60,000 to 160,000 hospitalizations and 6,000 to 10,000 deaths annually among patients aged ≥65 years.5 Patients who are elderly, immunocompromised, or who have underlying heart or lung conditions are at increased risk for symptomatic RSV infection and severe RSV-related disease, as are patients who live in long-term care facilities. A recent study using the RSV-Associated Hospitalization Surveillance Network found that, among adults aged ≥60 years who were hospitalized with RSV, 54.1% were aged 75 years or older, 17.2% were long-term care facility residents, and 18.6% had an immunocompromising condition; almost all patients had at least 1 underlying medical condition, with the most common being obesity, chronic obstructive pulmonary disease (COPD), congestive heart failure, and diabetes mellitus.6 Among these hospitalized patients, 17% required admission to the intensive care unit (ICU), and 4.7% died.

Recent data suggest that although RSV-associated hospitalization may be less common than COVID-19- or influenza-associated hospitalization, patients who are hospitalized with RSV may be more likely to experience severe disease than those who are hospitalized with other respiratory viruses.7 A prospective study enrolling 5784 adults aged ≥60 years hospitalized with acute viral respiratory illness found that patients hospitalized with RSV were more than twice as likely to require standard flow oxygen, high-flow nasal cannula oxygen, or noninvasive ventilation compared to those hospitalized with COVID-19 or influenza. Patients hospitalized with RSV were also approximately 1.5 times more likely to require ICU admission compared to those hospitalized with COVID-19 or influenza. Rates of invasive mechanical ventilation or death were not significantly different for patients with RSV versus COVID-19, but approximately 2 times greater among patients with RSV compared to those with influenza.

Until recently, the only option for RSV prevention was passive immunization with a monoclonal antibody (palivizumab); this option was only available to high-risk infants and young children, in part due to the significant cost burden associated with its use and the need for monthly administration during RSV season.8,9 However, several new options for RSV prophylaxis emerged in 2023, including a second monoclonal antibody (nirsevimab) and two RSV vaccines.10-12 The two RSV vaccines approved for use in the United States are Arexvy (RSVPreF3, manufactured by GSK) and Abrysvo (RSVpreF; manufactured by Pfizer).2 Arexvy was the first RSV vaccine to be released, gaining approval for use in patients aged ≥60 years in May 2023.12 Abrysvo was approved for use in the same patient population shortly afterward, and it became the first and only RSV vaccine approved for use in pregnant patients (to prevent RSV in infants) in August 2023.11,13

RSV Vaccine Development and Mechanisms of Protection
Attempts to develop an RSV vaccine began in the 1960s with a formalin-inactivated RSV vaccine.14 However, cases of vaccine-associated enhanced respiratory disease were reported with this vaccine; the majority of RSV-naive infants who received it experienced severe and, in two cases, fatal lung inflammation with their first natural RSV infection.14,15 These safety concerns led to a lack of further vaccine development for many years afterward, but an increased understanding of RSV and associated technological advances have allowed for further progress.14

The RSV virus is composed of 11 structural and non-structural proteins, including the fusion (F) glycoprotein.15 The F glycoprotein is a surface protein on the outer membrane of the virus that plays a key role in fusion of the viral and host cell membranes. The F glycoprotein has 2 antigenically distinct conformations, the prefusion conformation (preF) and the postfusion conformation (postF); change from the preF to the postF conformation can occur as a result of viral and cell membrane fusion or spontaneously via unknown mechanisms that initiate rearrangement to the energetically favorable postF conformation.16 Current vaccines against RSV use the stabilized preF protein as the vaccine antigen.15,17 The preF conformation is used because it is more immunogenic than the postF conformation and has been shown to induce the majority of highly neutralizing antibodies following natural RSV infection.16-18

Administration of a preF RSV vaccine is a form of active immunization, inducing an immune response against the RSV preF protein in the vaccinated individual.19,20 When the vaccine is administered to a pregnant patient, antibodies formed by the pregnant patient are transferred transplacentally to the fetus, leading to passive immunization of the infant as well.20

RSV Vaccine Characteristics
There are several key differences between the 2 available RSV vaccines, aside from their differing indications. Arexvy (RSVPreF3) contains a recombinant RSV preF protein antigen that is based on the RSV-A subtype; it also contains an AS01E adjuvant component.21 Abrysvo (RSVpreF) is a non-adjuvanted vaccine that contains recombinant RSV preF protein antigen based on both RSV-A and RSV-B subtypes.

Both vaccines are supplied in single-dose vials and require reconstitution with the accompanying diluents (adjuvant suspension for Arexvy or sterile water for injection for Abrysvo) prior to intramuscular administration.20,21 For both vaccines, a single 0.5 mL dose contains 120 mcg of the preF antigen component. Unreconstituted Arexvy and its diluent should be stored in the refrigerator at 2 to 8°C and protected from light; after reconstitution, the vaccine should be administered immediately, but it may also be stored refrigerated or at room temperature (up to 25°C) for up to 4 hours.21 Unreconstituted Abrysvo and its diluent should be stored in the refrigerator at 2 to 8°C. After reconstitution, the vaccine should be used immediately or stored at room temperature (15 to 30°C) for up to 4 hours. Reconstituted Abrysvo should not be stored in the refrigerator.

Both vaccines are contraindicated in patients with a history of severe allergic reaction to any component of the formulation.21 The vaccines can be administered to patients with minor acute illness, but vaccination should generally be deferred in patients with moderate to severe acute illness (with or without fever). Abrysvo carries an additional warning about the potential risk of preterm birth in pregnant patients; it is recommended to administer Abrysvo at 32 to 36 weeks gestation to avoid this risk.20

Clinical Data for Available RSV Vaccines
Approval trials for Arexvy and Abrysvo for their respective indications are summarized in Table 1 below. In patients aged ≥60 years, a single dose of Arexvy has been shown to prevent RSV-related acute respiratory infection, RSV-related lower respiratory tract disease, and severe RSV-related lower respiratory tract disease for 2 consecutive RSV seasons.22,23 Data for Abrysvo in patients aged ≥60 years were limited to a single RSV season at the time of writing; however, the RENOIR trial found that a single dose of Abrysvo prevented RSV-related lower respiratory tract illness and RSV-related acute respiratory illness in patients aged ≥60 years for 1 RSV season without significant safety concerns.24 The MATISSE trial examined the efficacy of Abrysvo for preventing RSV-related disease in infants.25 When a single dose of Abrysvo was administered to pregnant women between 24 and 36 weeks’ gestation, it reduced the risk of medically attended severe RSV-associated lower respiratory tract illness in infants for 180 days after birth.

Additional studies have specifically examined whether Arexvy and Abrysvo can be given concomitantly with other common vaccines. For Arexvy, one study found that coadministration with a quadrivalent influenza vaccine (Fluarix Quadrivalent or Fluarix Tetra) was noninferior to sequential administration of the vaccines (1 month apart) in terms of RSV-A neutralization titers and hemagglutination inhibition titers.26 Similarly, a study with Abrysvo found that coadministration with another quadrivalent influenza vaccine (Fluad Quad) was noninferior to sequential administration of the vaccines (1 month apart) in terms of RSV-A and RSV-B neutralization titers and hemagglutination inhibition titers.27 No significant safety concerns were identified with coadministration in either study.26,27 Abrysvo has also been studied for concomitant administration with the Tdap vaccine (Boostrix) in healthy, non-pregnant women.28 In this study, immune responses to RSV-A and RSV-B with concomitant Abrysvo and Tdap administration were noninferior to those observed with Abrysvo alone. Immune responses to diphtheria toxoid and tetanus toxoid with concomitant Abrysvo and Tdap administration were noninferior to those observed with Tdap alone, but noninferiority was not met for immune response to the pertussis component of the Tdap vaccine. The clinical significance of this finding remains unknown. Safety and tolerability were similar for Abrysvo alone and Abrysvo administered with Tdap.

Table 1. Overview of phase 3 approval trials for available RSV vaccines.22-25
Study design and durationSubjectsInterventionsResultsConclusions
Arexvy (RSVPreF3; GSK)
Papi 202322

AReSVi-006

MC, DB, PC, RCT

Follow-up through the end of the first RSV season in the Northern Hemisphere

Ison 202423

Follow-up through the end of the second RSV season in the Northern Hemisphere (≥1 RSV season in the Southern Hemisphere)		N=24,966 patients aged ≥60 years

Median age: 69.5 years

Approximately 39% had comorbidities associated with increased risk of severe RSV, including cardiorespiratory conditions in approximately 20% and endocrine or metabolic conditions in approximately 25%		Single dose of RSVPreF3 adjuvanted vaccine IM (n=12,467)

Saline placebo IM (n=12,499)

Injections were administered in the nondominant arm before the first RSV season began

Before the second RSV season, patients previously assigned to the RSVPreF3 group were rerandomized to receive a second RSVPreF3 dose (n=4966) or placebo (n=4991); patients previously assigned to the placebo group received a second placebo injection (n=10,033)		Primary:
RSV-related lower respiratory tract disease (confirmed by RT-PCR) during the first RSV season (median follow-up 6.7 months): 7 cases in the vaccine group vs. 40 cases in the placebo group; vaccine efficacy, 82.6% (96.95% CI, 57.9 to 94.1%)

Secondary:
Severe RSV-related lower respiratory tract disease during the first RSV season: 1 case in the vaccine group vs. 17 cases in the placebo group; vaccine efficacy 94.1% (95% CI, 62.4 to 99.9%)

≥1 episode of RSV-related acute respiratory infection during the first RSV season: 27 cases in the vaccine group vs. 95 cases in the placebo group; vaccine efficacy 71.7% (95% CI, 56.2 to 82.3%)

Vaccine efficacy was similar for both RSV subtypes (RSV-A and RSV-B)

Efficacy of a single RSVPreF3 dose over 2 RSV seasons (median follow-up, 17.8 months) was 67.2% (97.5% CI, 48.2 to 80%) for RSV-related lower respiratory tract disease and 78.8% (95% CI, 52.6 to 92%) for severe RSV-related lower respiratory tract disease

Efficacy of a first RSVPreF3 dose followed by revaccination 1 year later over 2 RSV seasons (median follow-up, 17.8 months) was 67.1% (97.5% CI, 48.1 to 80%) for RSV-related lower respiratory tract disease and 78.8% (95% CI, 52.5 to 92%) for severe RSV-related lower respiratory tract disease

Safety:
In the first RSV season, in the solicited safety population (n=1757), pain was the most common injection-site reaction (60.9% in the vaccine group vs. 9.3% in the placebo group) and fatigue was the most common systemic reaction (33.6% in the vaccine group vs. 16.1% in the placebo group); most solicited reactions were mild or moderate in severity and resolved within the 4-day solicitation period

In the first RSV season, in the exposed population (all patients), unsolicited AEs were reported in 33% of patients given the vaccine and 17.8% of patients given placebo; serious AEs were reported in 4.2% of vaccine recipients and 4% of placebo recipients; potential immune-mediated diseases were reported in 0.3% of patients in each treatment group; mortality rates were 0.4% and 0.5% for the vaccine and placebo groups, respectively

Safety of a revaccination dose prior to the second RSV season was similar to dose 1		A single dose of RSVPreF3 adjuvanted vaccine had an acceptable safety profile and prevented RSV-related acute respiratory infection, RSV-related lower respiratory tract disease, and severe RSV-related lower respiratory tract disease in patients aged ≥60 years for 2 RSV seasons.

Revaccination after 1 year did not provide additional efficacy benefit.
Abrysvo (RSVpreF; Pfizer)
Walsh 202324

RENOIR

MC, DB, PC, RCT

Follow-up through the end of the first RSV season		N=34,284 patients aged ≥60 years

Median age: 67 years

51.6% had a prespecified high risk condition, and 15.3% had ≥1 chronic cardiopulmonary condition		Single dose of RSVpreF vaccine IM (n=17,215)

Placebo IM (n=17,069)		Primary:
RSV-related lower respiratory tract illness (≥2 signs/symptoms lasting >1 day with RSV infection confirmed by RT-PCR) during the first RSV season (median follow-up, 7 months): 11 cases in the vaccine group vs. 33 cases in the placebo group; vaccine efficacy, 66.7% (96.66% CI, 28.8 to 85.8%)

RSV-related lower respiratory tract illness (≥3 signs/symptoms lasting >1 day with RSV infection confirmed by RT-PCR) during the first RSV season: 2 cases in the vaccine group vs. 14 cases in the placebo group; vaccine efficacy, 85.7% (96.66% CI, 32 to 98.7%)

Secondary:
First episode of RSV-related acute respiratory illness (≥1 symptom with RSV infection confirmed on RT-PCR) during the first RSV season: 22 cases in the vaccine group vs. 58 cases in the placebo group; vaccine efficacy 62.1% (95% CI, 37.1 to 77.9%)

Safety:
In the electronic diary subgroup of the safety population (n=7169), local reactions were more common among vaccine recipients (12% vs. 7% with placebo); systemic AE rates were similar between groups (27% and 26% for vaccine and placebo respectively); injection site pain was the most common local reaction (11% vs. 6% for vaccine and placebo respectively); fatigue (16% vs. 14%) and headache (13% vs. 12%) were the most common systemic AEs

AEs within 1 month of injection were reported by 9% of vaccine recipients and 8.5% of placebo recipients; reported AEs were similar between groups

Serious AEs were reported in 2.3% of patients in each group		A single dose of RSVpreF vaccine prevented RSV-related lower respiratory tract illness and RSV-related acute respiratory illness in patients aged ≥60 years for 1 RSV season without significant safety concerns.
Kampmann 202325

MATISSE

MC, DB, PC, RCT

Infants born to vaccinated mothers followed for 1 to 2 years after birth		N=7358 healthy pregnant women aged ≤49 years at 24 to 36 weeks’ gestation on the day of planned injection; patients had uncomplicated singleton pregnancies and no known increased risk of pregnancy complications

Median age: 29 years

Median gestation at time of injection: 31.3 weeks		Single dose of RSVpreF vaccine IM (n=3682 mothers; 3570 infants evaluated)

Placebo IM (n=3676 mothers; 3558 infants evaluated)		Primary:
Medically attended severe RSV-associated lower respiratory tract illness in infants within 90 days after birth: 6 cases in the vaccine group vs. 33 cases in the placebo group; vaccine efficacy, 81.8% (99.5% CI, 40.6 to 96.3%)

Medically attended severe RSV-associated lower respiratory tract illness in infants within 180 days after birth: 19 cases in the vaccine group vs. 62 cases in the placebo group; vaccine efficacy, 69.4% (97.58% CI, 44.3 to 84.1%)

Medically attended RSV-associated lower respiratory tract illness in infants within 90 days after birth: 24 cases in the vaccine group vs. 56 cases in the placebo group; vaccine efficacy, 57.1% (99.5% CI, 14.7 to 79.8%)

Medically attended RSV-associated lower respiratory tract illness in infants within 180 days after birth: 57 cases in the vaccine group vs. 117 cases in the placebo group; vaccine efficacy, 51.3% (97.58% CI, 29.4 to 66.8%)

Secondary:
Vaccine efficacy was 67.7% (99.17% CI, 15.9 to 89.5%) for RSV-associated hospitalization in infants within 90 days after birth and 56.8% (99.17% CI, 10.1 to 80.7%) for RSV-associated hospitalization in infants within 180 days after birth

Safety:
Local reactions were more common among maternal participants who received the vaccine vs. those who received placebo; the most common local reaction was injection site pain (41% of maternal vaccine recipients vs. 10% of maternal placebo recipients)

Systemic AEs reported more frequently among maternal participants who received the vaccine were muscle pain (27% vs. 17% with placebo) and headache (31% vs. 28% with placebo)

AEs within 1 month of injection were reported by 13.8% of maternal vaccine recipients and 13.1% of maternal placebo recipients; AEs within 1 month after birth were reported in 37.1% of infants in the vaccine group and 34.5% of infants in the placebo group

Serious AEs within 6 months after injection were similar between groups for maternal participants; serious AEs within 24 months after birth were similar between groups for infants		A single dose of RSVpreF vaccine administered during pregnancy prevented medically attended severe RSV-associated lower respiratory tract illness in infants, with no safety concerns identified. This trial was halted early when the statistical success criterion for vaccine efficacy was met for one of the two primary efficacy end points; the statistical success criterion was not met for medically attended RSV-associated lower respiratory tract illness in infants within 90 days after birth.
Abbreviations: AE=adverse event; CI=confidence interval; DB=double-blind; IM=intramuscular; MC=multicenter; PC=placebo-controlled; RCT=randomized controlled trial; RSV=respiratory syncytial virus; RT-PCR=reverse-transcriptase polymerase chain reaction.

Recommendations for RSV Vaccination
The CDC and the Advisory Committee on Immunization Practices (ACIP) recommend that adults aged ≥60 years may receive a single dose of RSV vaccine to protect against severe RSV; a shared clinical decision-making process should be used when selecting patients for vaccination.2,5,21 The decision to vaccinate elderly patients against RSV should be based on the patient’s health status and risk of severe RSV disease, the healthcare provider’s clinical judgment, the patient’s preferences, and the characteristics of the vaccine.21 Patients at increased risk of severe RSV disease are most likely to benefit from vaccination.5,21 This includes frail patients, patients of advanced age, patients living in nursing homes or other long-term care facilities, and patients with any of the following underlying chronic conditions: lung disease (e.g., COPD, asthma), cardiovascular disease (e.g., heart failure, coronary artery disease), kidney or liver disorders, neurologic or neuromuscular conditions, hematologic disorders, diabetes mellitus, or moderate or severe immune compromise. Benefits of vaccination are maximized when the vaccine is given in the late summer or early fall, just prior to RSV season.21 Currently, annual RSV vaccination is not recommended, but studies are ongoing to determine whether revaccination is needed over time.2,21 Current data suggest that protection associated with a single RSV vaccine dose lasts for at least 2 RSV seasons.21

The CDC and ACIP also recommend a one-time RSV vaccine dose for people who are 32 to 36 weeks pregnant, to protect their infants from RSV-associated lower respiratory tract infection.2,4 Alternatively, a monoclonal antibody (nirsevimab) may be administered to the baby after birth to prevent RSV. Administration of both the vaccine and the monoclonal antibody is not necessary in most cases. When choosing between these preventive strategies, providers should discuss the advantages and disadvantages of each strategy with the patient (see Table 2) and take patient preference into account. Vaccination against RSV should occur seasonally; in most of the continental United States, the recommended time frame for vaccination is September through January, but seasonality may differ in certain areas, and providers should follow local guidance regarding the timing of administration.

Table 2. Advantages and Disadvantages of RSV Prevention Modalities in Infants.4
Maternal RSV vaccineInfant nirsevimab administration
AdvantagesProvides protection immediately after birth

May be more resistant to mutations in the F protein, because vaccination results in a polyclonal immune response		Protection may wane more slowly than protection from the maternal RSV vaccine

Assures direct receipt of antibodies rather than relying on placental transfer

No risk for adverse pregnancy outcomes
DisadvantagesPotential for reduced protection if fewer antibodies are produced or transferred from the pregnant person to the baby (e.g., pregnant person is immunocompromised or infant is born soon after vaccination)

Potential risk of preterm birth and hypertensive disorders of pregnancy		Potentially limited availability during RSV season

Requires infant injection
Abbreviations: RSV=respiratory syncytial virus.

Conclusion
Respiratory syncytial virus is a significant cause of morbidity and mortality in infants, very young children, and elderly patients. In 2023, two vaccines against RSV were approved for use in the United States. Both vaccines are approved to prevent RSV-related lower respiratory tract disease in patients aged ≥60 years; one vaccine, Abrysvo, is also approved for administration to pregnant patients to prevent RSV-related lower respiratory tract disease in infants from birth to 6 months of age. For patients aged ≥60 years, the CDC and ACIP currently recommend that a shared clinical decision-making process be used when deciding whether to administer a single dose of RSV vaccine. For prevention of RSV-related disease in infants, the CDC and ACIP recommend either a maternal RSV vaccine or administration of nirsevimab to the infant after birth; the choice between these two modalities should be based on patient preference after a discussion of the advantages and disadvantages associated with each.

References

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  11. U.S. FDA approves ABRYSVO™, Pfizer’s vaccine for the prevention of respiratory syncytial virus (RSV) in older adults. Pfizer. Published May 31, 2023. Accessed March 14, 2024. https://www.pfizer.com/news/press-release/press-release-detail/us-fda-approves-abrysvotm-pfizers-vaccine-prevention
  12. FDA approves first respiratory syncytial virus (RSV) vaccine. U.S. Food and Drug Administration. Published May 3, 2023. Updated May 4, 2023. Accessed March 14, 2024. https://www.fda.gov/news-events/press-announcements/fda-approves-first-respiratory-syncytial-virus-rsv-vaccine
  13. FDA approves first vaccine for pregnant individuals to prevent RSV in infants. U.S. Food and Drug Administration. Published August 21, 2023. Updated August 22, 2023. Accessed March 14, 2024. https://www.fda.gov/news-events/press-announcements/fda-approves-first-vaccine-pregnant-individuals-prevent-rsv-infants
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  25. Kampmann B, Madhi SA, Munjal I, et al. Bivalent prefusion F vaccine in pregnancy to prevent RSV illness in infants. N Engl J Med. 2023;388(16):1451-1464. doi:10.1056/NEJMoa2216480
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  28. Peterson JT, Zareba AM, Fitz-Patrick D, et al. Safety and immunogenicity of a respiratory syncytial virus prefusion F vaccine when coadministered with a tetanus, diphtheria, and acellular pertussis vaccine. J Infect Dis. 2022;225(12):2077-2086. doi:10.1093/infdis/jiab505

Prepared by:
Laura Koppen, PharmD, BCPS
Clinical Assistant Professor, Drug Information Specialist
University of Illinois at Chicago College of Pharmacy

April 2024

The information presented is current as of March 14, 2024. This information is intended as an educational piece and should not be used as the sole source for clinical decision-making.