RSV vaccines for older adults: who is eligible, and what the trials measured

Respiratory syncytial virus, long thought of as a childhood illness, causes substantial hospitalisation and death in older adults, and two vaccines are now recommended to prevent it — with eligibility that is age- and risk-based rather than universal [s3]. In the United States, guidance recommends a single dose for all adults aged 75 and older, and for adults aged 50–74 who are at increased risk because of chronic heart or lung disease, diabetes, weakened immunity or other conditions [s3]. This is the adult-eligibility question, distinct from the separate maternal RSV vaccine given in pregnancy to protect newborns.

What the pivotal trials showed

Two large randomised, placebo-controlled trials established efficacy in older adults, using different products and slightly different endpoints — so their headline numbers should not be read as a head-to-head comparison [s1][s2].

The AReSVi-006 trial of the RSVPreF3 OA vaccine, in adults 60 and older, found efficacy against RT-PCR-confirmed RSV-related lower respiratory tract disease of 82.6% (96.95% confidence interval 57.9 to 94.1) over a median 6.7 months, with 7 cases in the vaccine group versus 40 in placebo [s1]. Efficacy against severe RSV lower-respiratory disease was 94.1% [s1]. The RENOIR trial of the bivalent RSVpreF vaccine, also in adults 60 and older, used a stricter case definition — lower-respiratory illness with at least two signs or symptoms — and found efficacy of 66.7% (96.66% CI 28.8 to 85.8), with 11 cases in the vaccine group versus 33 in placebo [s2]. Both trials reported acceptable short-term safety, with more local reactions after vaccine than placebo but similar rates of systemic events [s2].

The apparent gap between 82.6% and 66.7% is driven substantially by the different endpoints and confidence intervals, both of which were wide because RSV cases accrued slowly over a single season [s1][s2]. The defensible summary is that both vaccines substantially reduced RSV lower-respiratory illness in their first season, by roughly two-thirds to four-fifths depending on product and definition [s1][s2].

Why eligibility is targeted, not universal

Unlike childhood vaccines given to everyone, the adult RSV vaccines are recommended by age and risk because the disease burden is concentrated in older and chronically ill adults, and because a single dose is expected to provide multi-season rather than annual protection [s3]. The lowered high-risk threshold to age 50 reflects evidence that certain younger adults with lung or heart disease also face meaningful RSV risk [s3].

What remains uncertain

The pivotal trials reported first-season efficacy; how durable protection is across two or more RSV seasons, and when or whether a repeat dose is warranted, are questions that longer follow-up is still resolving [s1][s2]. The wide confidence intervals — particularly RENOIR's lower bound near 29% — reflect the modest number of cases and mean the true efficacy for the stricter endpoint is estimated with less precision than the point figure suggests [s2]. This is an informational summary of guideline recommendations and trial results, not medical advice; eligibility is a decision for a clinician.