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An adenoviral vector vaccine against respiratory syncytial virus (RSV) in older adults was safe and effective, particularly against severe disease, a researcher said.

Janssen's Ad.26 RSV preF-based vaccine showed 80% vaccine efficacy (94.2% CI 52.2%-92.9%) against RSV with at least three lower respiratory tract infection (LRTI) symptoms, and 69.8% efficacy (94.2% CI 43.7%-84.7%) against RSV with at least two LRTI symptoms or one LRTI symptom and one systemic symptom, reported Ann Falsey, MD, of the University of Rochester in New York.

The vaccine was also well-tolerated, with no safety signals, and elicited "robust and durable humoral and cellular immune responses," Falsey said at a late-breaking presentation at the virtual IDWeek.

She noted that while RSV can be mainly known as a pediatric disease, older adults, ages 65 and up, are hospitalized with RSV at a higher rate than the youngest age group. In fact, Falsey pointed to prior research that found the rate of RSV-related hospitalization was 137/256 per 100,000 among older adults, which was 11 times the rate of patients in lower age brackets, "clearly demonstrating age is a risk factor for severe RSV disease," she noted.

Not only that, but an estimated 177,000 hospitalizations and 14,000 deaths occur in adults, ages 65 and up, in the U.S. annually due to RSV, Falsey added.

There is no licensed vaccine to prevent RSV, but she explained how the vaccine combines two components: the replication-deficient adenovirus vector used in the COVID vaccine and the pre-fusion F gene.

was a phase IIb concept trial at 40 U.S. sites where adults (ages 65 and up), including those with "stable" chronic disease, were randomized 1:1, stratified for disease risk and age. The trial began in August 2019 and is slated to last over the course of three RSV seasons, for a total of 2.6 years during which time participants will be surveilled for acute respiratory infections.

Falsey presented data on the first season of the trial, which she noted was "cut a bit short" due to the COVID pandemic in March 2020.

Every week, participants were prompted to report any symptoms, after which they received a telephone call and an illness evaluation, she said. They recorded their symptoms in a symptom diary.

Participants took a mid-turbinate nasal swab at home between days 1 and 2 of symptoms, which was repeated between days 3 and 5 by a staffer at the clinic when they came in. Sputum was also collected, and subjects were followed to day 29.

A case was defined as laboratory-confirmed RSV via RT-PCR in nasal or sputum samples, and RSV symptoms included both LRTI symptoms, such as cough, dyspnea, wheezing and sputum production, and systemic symptoms, like fever.

The study had three primary outcomes:

• Case definition 1: ≥3 new onset or worsening LRTI symptoms
• Case definition 2: ≥2 new onset or worsening LRTI symptoms
• Case definition 3: ≥2 LRTI symptoms or ≥1 new onset or worsening systemic symptoms

Overall, 5,782 patients were enrolled in the study. They had a median age of 71; 58% were women and 93% were white. Falsey noted that a little less than a quarter of participants were ages 75-84, and about a quarter had risk factors for chronic heart or lung disease that predisposed them to increased risk of RSV.

Vaccine efficacy was 80% for case definition 1, 75% (94.2% CI 50.1%-88.5%) for case definition 2, and 69.8% for case definition 3.

"One could say the vaccine was 69.8% effective to prevent any symptomatic, acute [RSV] illness," she added.

A summary of safety results from the 700-person safety cohort found there were no vaccine-related serious adverse events (AEs), though 3.2% of vaccine participants and 0.6% of placebo participants had solicited grade ≥3 AEs. The most frequent systemic events were fatigue, myalgia, and headache.

Falsey said that given these results, the phase III EVERGREEN study of the vaccine is currently enrolling.

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