Respiratory syncytial virus (RSV) infection is a common cause of respiratory illnesses in the lower respiratory tract worldwide. It poses a significant threat, particularly to infants, young children, and older individuals. Older adults, who may be frail or have underlying health conditions, are especially vulnerable to severe RSV disease. In the United States and Europe, approximately 3 to 7% of healthy older adults contract RSV each year, leading to an estimated 177,000 hospitalizations and 14,000 deaths annually in the United States alone [1-2].
When older adults are hospitalized with RSV disease, the severity of the illness is notable. A significant 18% of these individuals require admission to an intensive care unit with a one-year mortality rate approaching 26% [3]. Unfortunately, the diagnosis of RSV infection in adults is likely underreported since it is not legally mandated to report RSV infections in most jurisdictions, unlike influenza. Moreover, routine testing for RSV is not commonly conducted, making the accuracy of diagnosis uncertain.
Another important aspect to consider is that older adults exhibit higher levels of RSV shedding compared to younger adults, and the shedding persists for a longer duration. As a result, the overall burden of RSV-related illness in older adults is significant. Therefore, there was an urgent and unmet medical need to develop a vaccine that can protect this vulnerable population from RSV-induced lower respiratory tract illness.
RSV Vaccine Trials
The bivalent RSV prefusion F protein-based (RSVpreF) vaccine, which contains stabilized prefusion F glycoproteins from the two main antigenic subgroups (RSV A and RSV B), has shown promising results in clinical studies. In phase 1-2 trials involving adults, vaccination with RSVpreF formulations at a 120-μg dose significantly increased RSV neutralizing titers and exhibited an acceptable safety profile [4-6]. Furthermore, in an RSV challenge study with healthy individuals aged 18 to 50, the vaccine demonstrated an efficacy of 87% (95% confidence interval [CI], 54 to 96) in preventing symptomatic RSV infection confirmed by detectable viral RNA on consecutive days [7].
Based on the positive safety, immunogenicity, and efficacy data, the RSVpreF vaccine advanced to two important phase 3 trials. The first trial, known as RENOIR (RSV Vaccine Efficacy Study in Older Adults Immunized against RSV Disease), involved adults aged 60 and above, aiming to evaluate the efficacy and safety of the vaccine in preventing RSV-associated lower respiratory tract illness. The second trial, called MATISSE (Maternal Immunization Study for Safety and Efficacy), focused on assessing the efficacy and safety of maternal RSVpreF vaccination in preventing RSV-related lower respiratory tract illness in infants.
RENOIR Trial
A phase 3 trial was conducted to evaluate the effectiveness and safety of the investigational bivalent RSV prefusion F protein-based (RSVpreF) vaccine in older adults (≥60 years of age). Participants were randomly assigned to receive either the vaccine or a placebo [8].
The primary goals were to assess the vaccine's effectiveness in preventing seasonal RSV-associated lower respiratory tract illness with at least two or three signs or symptoms. The secondary goal was to evaluate its effectiveness against RSV-associated acute respiratory illness.
At the interim analysis, a total of 34,284 participants had received either the RSVpreF vaccine or the placebo. The vaccine group demonstrated a significantly lower incidence of RSV-associated lower respiratory tract illness with at least two or three signs or symptoms compared to the placebo group. The vaccine's effectiveness was reported at 66.7% (CI: 28.8 to 85.8) and 85.7% (CI: 32.0 to 98.7) for the respective goals. Additionally, the vaccine showed a 62.1% (CI: 37.1 to 77.9) effectiveness in preventing RSV-associated acute respiratory illness.
The occurrence of local reactions was higher in the vaccine group compared to the placebo group, while systemic events were similar between the two groups. Adverse events reported within one month after injection were comparable, and severe or life-threatening adverse events were rare in both vaccine and placebo recipients. In the vaccine group, there were three notable adverse events associated with the study product: one case of Guillain-Barré syndrome, one case of Miller-Fisher syndrome, and one instance of a delayed allergic reaction.
MATISSE Trial
A phase 3 double-blind trial was conducted in 18 countries to determine whether administering the bivalent RSVpreF vaccine during pregnancy could reduce the incidence of respiratory syncytial virus (RSV)-associated lower respiratory tract illness in newborns and infants [9].
Pregnant women at 24 to 36 weeks' gestation were randomly assigned to receive a single intramuscular injection of either the RSVpreF vaccine or a placebo. The primary effectiveness goals were medically attended severe RSV-associated lower respiratory tract illness and medically attended RSV-associated lower respiratory tract illness in infants within 90, 120, 150, and 180 days after birth.
The evaluation included 3,570 infants from the vaccine group and 3,558 from the placebo group. At the interim analysis, medically attended severe lower respiratory tract illness within 90 days after birth occurred in 6 infants from the vaccine group compared to 33 infants from the placebo group, resulting in a vaccine effectiveness of 81.8% (99.5% CI: 40.6 to 96.3). Within 180 days after birth, the vaccine effectiveness was 69.4% (97.58% CI: 44.3 to 84.1) with 19 cases in the vaccine group and 62 cases in the placebo group.
Regarding medically attended RSV-associated lower respiratory tract illness, the vaccine showed a vaccine effectiveness of 57.1% (99.5% CI: 14.7 to 79.8) within 90 days after birth. However, these results did not meet the statistical success criterion.
No safety concerns were identified in maternal participants or infants and toddlers up to 24 months of age. The incidence of adverse events was similar between the vaccine and placebo groups.
FDA Approval
The U.S. Food and Drug Administration (FDA) has granted approval for RSVpreF vaccine (Arexvy), marking it as the first-ever vaccine for the Respiratory Syncytial Virus (RSV) in the country. Specifically aimed at preventing lower respiratory tract disease caused by RSV, the vaccine is designed for individuals aged 60 and above. To ensure safety and efficacy, the FDA mandates a postmarketing study by the company, aiming to examine potential serious risks associated with Guillain-Barré syndrome and acute disseminated encephalomyelitis (ADEM). The company also plans to study the vaccine's impact on atrial fibrillation as part of its postmarketing commitments.
Will you recommend the RSV vaccine for adults 60 years and above once available in your country?
0%Yes
0%No
0%Awaiting post-marketing safety data
Conclusion
The FDA's approval of Arexvy in adults 60 years or above, the first RSV vaccine, is a significant milestone in global health. Demonstrating safety and effectiveness in reducing RSV-associated illnesses in both older adults and infants through maternal vaccination, it provides a new tool to combat this serious disease. The mandatory postmarketing studies will ensure continued safety monitoring, while its approval for use during pregnancy is still underway.
REFERENCES:
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Korsten K, Adriaenssens N, Coenen S, et al. Burden of respiratory syncytial virus infection in community-dwelling older adults in Europe (RESCEU): an international prospective cohort study. Eur Respir J 2021;57:2002688-2002688.
Ackerson B, Tseng HF, Sy LS, et al. Severe morbidity and mortality associated with respiratory syncytial virus versus influenza infection in hospitalized older adults. Clin Infect Dis 2019;69:197-203.
Falsey AR, Walsh EE, Scott DA, et al. Phase 1/2 randomized study of the immunogenicity, safety, and tolerability of a respiratory syncytial virus prefusion F vaccine in adults with concomitant inactivated influenza vaccine. J Infect Dis 2022;225:2056-2066.
Walsh EE, Falsey AR, Scott DA, et al. A randomized phase 1/2 study of a respiratory syncytial virus prefusion F vaccine. J Infect Dis 2022;225:1357-1366.
Baber J, Arya M, Moodley Y, et al. A phase 1/2 study of a respiratory syncytial virus prefusion F vaccine with and without adjuvant in healthy older adults. J Infect Dis 2022;226:2054-2063.
Schmoele-Thoma B, Zareba AM, Jiang Q, et al. Vaccine efficacy in adults in a respiratory syncytial virus challenge study. N Engl J Med 2022;386:2377-2386.
Walsh EE et al. Efficacy and safety of a bivalent RSV prefusion F vaccine in older adults. N Engl J Med 2023 Apr 20; 388:1465. (https://doi.org/10.1056/NEJMoa2213836. opens in new tab)
Kampmann B et al. Bivalent prefusion F vaccine in pregnancy to prevent RSV illness in infants. N Engl J Med 2023 Apr 20; 388:1451. (https://doi.org/10.1056/NEJMoa2216480. opens in new tab)