RSV vaccine effective across two seasons

The respiratory syncytial virus (RSV) vaccine by GSK demonstrated sustained effectiveness of about 67 percent among adults 60 years or older across two full RSV seasons in a phase III study, says an infectious disease expert who reported findings at IDWeek 2023.

Vaccine effectiveness (VE) against RSV-lower respiratory tract disease (LRTD) over two seasons was 67.2 percent (97.5 percent confidence interval [CI], 48.2–80 percent) for a single dose and 67.1 percent (97.5 percent CI, 48.1–80 percent), among individuals who received two doses over two seasons, said Dr Michael Ison, chief of the Respiratory Diseases Branch at the National Institute of Allergy and Infectious Diseases, Rockville, Maryland, US, during his presentation. [IDWeek 2023, abstract 1936]

“RSV is a major cause of hospitalization and mortality in older adults, resulting in over 177,000 hospitalizations due to RSV and over 14,000 deaths per year,” he reported.

“While the disease can occur in any older adult, it is worse in patients over 65 years of age, those with underlying comorbid conditions including primary vascular, lung, kidney and liver disease, as well as diabetes, and patients who are immunocompromised,” Ison added.

VE across two RSV seasons

Ison and his team sought to assess the efficacy of the RSV vaccine across two RSV seasons in a phase III, placebo-controlled multicountry trial. Included were adults 60 years or older who were randomly assigned to the vaccine or placebo prior to the first RSV season.

Vaccinated participants were reassigned to receive a second dose of the vaccine or placebo before the second RSV season.

VE against first occurrence of RSV-LRTD, severe RSV-LRTD, RSV-LRTD by age, baseline comorbidity and frailty status, and RSV-related acute respiratory illness were assessed across the two seasons.

Nearly 25,000 participants were included in the VE analyses (6,242 received two doses, 6,227 received one dose, 12,498 received a placebo twice).

Robust vaccine response

There was not much of a boosting effect after a second dose. And this Ison found as surprising. “Another study assessing antibody levels among patients who received either a single dose or multiple doses of the vaccine showed that there were relatively similar levels at a relatively high titre at month 12,” he shared.

“What this tells us is that we have generated a pretty robust vaccine response that’s maintained at least for greater than a year,” he pointed out.

Additionally, the study demonstrated sustained VE against severe RSV-LRTD, RSV-LRTD among adults 60–79 years of age and those with at least one baseline comorbidity, pre-frail patients, and against RSV-related acute respiratory illness.

Moving forward

More studies are ongoing to assess the best timing for revaccination, said Ison. One study is testing people 50–59 years of age, including those with underlying comorbidities. Results from two other trials testing co-administration with influenza vaccines are expected to be out soon.

The vaccine (Arexvy) is US-FDA approved to prevent LRTD cause by RSV in people 60 years or older.  It is one of the two licensed RSV vaccines in the US.

The approval was based on the pivotal AReSVI-006 (Adult Respiratory Syncytial Virus) study showing that the vaccine reduced the risk of RSV-related LRTD by 82.6 percent and severe RSV-related LRTD (preventing normal, everyday activities) by 94.1 percent. Additionally, efficacy was 94.6 percent in older adults with at least one underlying medical condition of interest, such as certain cardiorespiratory and endocrine-metabolic conditions.