Abrysvo Shows Strong Immune Response and Safety in Older Adults Over Two RSV Seasons

One month after receiving the respiratory syncytial virus prefusion F (RSVpreF), or Abrysvo, vaccine, folks ages 60 and older displayed high levels of RSV antibodies, which resulted in maintaining a strong safety profile over two seasons, according to findings published in Clinical Infectious Diseases.

RSV is a major cause of lower respiratory tract infections (LRTI) in older adults, especially those who are vulnerable and have underlying chronic conditions.

Abrysvo is a bivalent, stabilized prefusion F vaccine designed to protect against both major RSV subtypes, RSV-A and RSV-B.

It has been approved for use in adults ages 60 and older, those ages 18 to 59 who are at increased risk for RSV-related LRTI and infants through maternal vaccination.

A past study found that RSV accounted for 1% to 10% of influenza-like acute respiratory infections in those aged 50 and older worldwide.

In the U.S. alone, RSV leads to about 60,000 to 160,000 hospitalizations and 6,000 to 10,000 deaths annually among adults aged 65 and older, the study said.

However, due to limited RSV testing and inconsistent reporting, the true burden of RSV in adults may be unclear.

Researchers of the two-season Infectious Diseases study randomly assigned participants 1:1 to receive either a dose of Abrysvo or a placebo.

A key objective was to evaluate immune response one month after vaccination and before the second RSV season in a group of participants spanning from the Northern (USA, Canada, Japan, Finland and Netherlands) and Southern Hemispheres (Argentina and South Africa).

Based on the previous RENOIR trial published in 2023, this current study included adults aged 60 and older with stable health conditions across 241 sites in both hemispheres.

The flu and COVID-19 vaccines were also given during this period to participants who wished to have them.

Participants were observed for two seasons, from August 31, 2021, to December 18, 2023, to evaluate vaccine efficacy, its safety and the increase in antibody levels, or the geometric mean fold rise (GMFR), against RSV-A and RSV-B variants.

Out of 36,862 participants — 18,574 receiving Abrysvo and 18,288 receiving a placebo — one month after vaccination, the GMFR was 12.1, indicating a strong immune response.

Although antibody levels decreased by the second RSV season, they remained significantly higher than pre-vaccination levels, with a GMFR of 4.7.

The immune response was consistent across different age groups, with GMFRs for RSV-A and RSV-B ranging from 12.0 to 13.0 among those ages 60 to 69, 70 to 79 and 80 and older.

In addition, participants with pre-existing chronic conditions displayed antibody responses comparable to those without these conditions, with GMFRs ranging from 11.4 to 14.4.

The vaccine also demonstrated a strong safety profile and maintained its effectiveness over two RSV seasons.

Aside from the study’s robust results, one of its main strengths was its large sample size, which included over 36,000 participants, resulting in a clear evaluation of vaccine efficacy and safety.

The study also included a diverse group of participants from different parts of the world.

In addition, the vaccine remained effective over two RSV seasons, all while the main virus strain changed from RSV-B in the first season to RSV-A in the second.

Another key strength was that Abrysvo was safely co-administered flu and COVID-19 vaccines.

However, the study has limitations.

For example, the COVID-19 pandemic was still in occurrence during the first monitored RSV season, when social distancing and masking may have reduced RSV transmission, potentially affecting the study’s results.

Additionally, the vaccine's efficacy in participants and younger adults with pre-existing conditions was not directly assessed, as these groups were excluded from the trial.

While the study displayed strong immune responses, it remains unclear how long the protection from Abrysvo lasts beyond two RSV seasons.

Researchers suggest further investigation into the long-term effectiveness of Abrysvo and that new studies should look into any benefits of revaccination, including whether spacing vaccine doses more than two years apart provides added protection.

Future studies should confirm the vaccine’s effectiveness in older adults, particularly those aged 70 and older, who are at higher risk for severe RSV illness.

Lastly, it’s suggested that future research should explore vaccine effectiveness and safety in those with pre-existing conditions.