For older adults, the vaccine against respiratory syncytial virus (RSV) appears to be most effective in the first year after administration, according to new research that shows the benefits of the immunization fall roughly 60% within about 1.5 years.

The database analysis showed that among adults aged 60 years or older, the effectiveness of the RSV vaccine at preventing infections fell from 71% at the 4-month mark to 40% 19 months after receipt.

For clinicians, “the big takeaway is that the RSV vaccine works well, especially in the first year, and remains worth recommending to older patients, especially those at higher risk,” said Kersten Bartelt, RN, a research clinician at Epic Research, an arm of the records company, who helped conduct the analysis.

Bartelt and her colleagues analyzed data from more than 1 million adults aged 60 years or older who underwent RSV lab tests at 1700 hospitals and 40,000 clinics in the US, Lebanon, and Saudi Arabia during the 2024-2025 respiratory virus season. The study was completed by two research teams that worked independently and came to similar conclusions, according to the company.

The effectiveness of the vaccine in preventing RSV-related hospitalizations declined over approximately 1 year, from 73% at 4 months after immunization to 44% by 19 months. Effectiveness against RSV-related ED visits followed a similar trend, falling from 71% to 46% over the same period.

“We know that vaccine protection tends to fade over time, so the drop after 12 months matches what we expected,” Bartelt told Medscape Medical News.

Emergency department (ED) visits and hospitalizations for RSV were also twice as high among individuals vaccinated 1 year to 19 months prior to their visit compared with those vaccinated in the year prior.

However, people who never received an RSV vaccine had three times as many ED visits as those who had received a vaccination more recently.

The vaccine is not currently recommended as an annual shot, but a single dose is generally recommended for adults aged 75 years or older and those aged 60-74 years who may be at increased risk for infection, according to the CDC.

Data from the 2023-2024 respiratory virus season, when the vaccine was first recommended, indicate only about 22% of adults aged 60 years or older were vaccinated against RSV.

Bartelt said more data are needed to determine a regular schedule for routine RSV vaccination, including how long protection lasts, whether boosters help, and how the vaccine performs in different subgroups, such as those with weaker immune systems.

Three RSV vaccines are currently available: Arexvy and Abrysvo, which were approved in 2023, and mResvia, approved in 2024. The CDC states no preference among them.

Long-term effectiveness data for mResvia are limited because of its recent approval. However, Abrysvo has shown efficacy of nearly 89% against lower respiratory tract disease in an ongoing study. Arexvy showed efficacy of 83% against RSV-associated hospitalizations and protection against lower respiratory tract disease with some waning over the first 2 years after vaccination, according to the CDC.

Some barriers to RSV vaccination include lack of awareness among older adults, lack of ready availability in some clinics, and uncertain insurance coverage, Bartelt told Medscape Medical News.

In the Clinic

“Information regarding vaccine effectiveness and duration of protection is important as experience with the RSV vaccine grows,” said Shirin Mazumder, MD, an infectious diseases specialist and an associate professor at The University of Tennessee Health Science Center in Memphis, Tennessee, who was not involved in the study.

Given that the RSV vaccine is still relatively new, additional data from the new study give clinicians a better understanding of what to expect with the vaccine and how best to counsel patients, Mazumder said.

“Educating older patients on the existence and importance of the RSV vaccine is necessary to reduce the risk of serious illness and complications,” Mazumder said. “The burden of RSV infection among older adults is significant; upward of 180,000 adults aged 50 or older are hospitalized, and up to 10,000 older adults die each year.”

The study was conducted by Epic Research, and the authors are employed by Epic.

Mazumder had no financial conflicts to disclose.