What are the known long-term safety results past 1–2 years for mRESVIA?

The short version: mRESVIA has no long-term safety data past the roughly 18-month follow-up of a single manufacturer-funded trial, and that trial was not designed to detect rare or delayed harms.

The ConquerRSV trial followed participants for a median of 3.7 months for the primary safety analysis, with an extended follow-up to about 18 months for efficacy [1]. That extended phase reported no new safety signals, but it compared the vaccinated group only against the trial's placebo group, not against a truly unvaccinated population over years [1]. The trial was too small to detect rare events like Guillain-Barré syndrome; the manufacturer's own review acknowledged this limitation [1].

What is not known is substantial. No data exists on outcomes past 18 months, so questions about cumulative immune effects, waning protection requiring revaccination, or late autoimmune phenomena are simply unanswered [1]. The waning efficacy itself—from 83.7% to about 50% at 18 months—means the question of repeat dosing is live, and no long-term safety data exists for that scenario either [1].

The evidence base is one manufacturer-run trial with short follow-up, no unvaccinated comparison group beyond the blinded phase, and no post-marketing surveillance data yet. That is not a safety signal, but it is also not evidence of safety. It is an absence of evidence, and the absence is the finding.

Confidence: high that no long-term safety data exists; low confidence in any claim of long-term safety, because none has been studied.