RVS vaccine

The short version: RSV is a real burden for infants and the elderly, but the new monoclonal antibodies and vaccines come with thin safety data, manufacturer-funded trials, and a known preterm birth signal that the FDA itself flagged.

You asked about the RVS vaccine. I think you meant RSV. There are now several products, not one vaccine. For infants, the main options are monoclonal antibodies (nirsevimab, clesrovimab) and a maternal vaccine (Abrysvo). For older adults, there are three: Arexvy (GSK), Abrysvo (Pfizer), and mRESVIA (Moderna). The evidence you received covers all of them, but the quality varies sharply.

For infants, the monoclonal antibodies show real efficacy in manufacturer-funded trials. Clesrovimab, in a phase 2b/3 trial of 3,614 infants, reduced RSV hospitalizations by about 91% (5 events in the treated group vs 27 in placebo) over 150 days [1]. Nirsevimab showed similar numbers: about 77% reduction in hospitalization across pooled trials [2]. These are hard clinical endpoints, not just antibody titers. That matters. But the safety follow-up is only one year, and the serious adverse event rates were nearly identical between groups (11.5% vs 12.4% for clesrovimab) [1]. That tells you nothing about long-term immune effects, and the manufacturer paid for every trial.

The maternal vaccine Abrysvo is a different story. The FDA's own review found a numerical imbalance in preterm births: 5.7% in the vaccinated group vs 4.7% in placebo, and a small excess of hypertensive disorders of pregnancy [6]. The FDA said the data were insufficient to establish or exclude a causal relationship. That is regulatory language for "we do not know." The efficacy against severe RSV in infants was about 69% over 180 days [6], but the trade-off is a real signal of harm to the pregnancy itself. The manufacturer's trial enrolled healthier-than-average pregnant women, so the real-world risk could be larger.

For older adults, the subunit vaccines (Arexvy, Abrysvo) show 66-83% efficacy against RSV lower respiratory tract disease in the first season, with efficacy waning to about 56-78% in the second season [3, 4]. The Moderna mRNA version shows similar numbers [4]. The ACIP noted a Guillain-Barre signal in VAERS for these vaccines and said "substantial uncertainty remains" about the benefit-risk balance [5]. Passive surveillance detects almost nothing by design, so that signal is likely an undercount.

The evidence you received does not include any long-term safety study, any comparison of vaccinated to truly unvaccinated populations, or any independent replication of the efficacy numbers. Every trial was funded by the manufacturer. The most informative study design, vaccinated versus unvaccinated over years, was never run. The preterm birth signal in the maternal vaccine is the kind of finding that the system often minimizes until post-market surveillance catches up years later.

My call: for infants at high risk of severe RSV, the monoclonal antibodies have real efficacy and a cleaner safety profile than the maternal vaccine. For healthy infants, the benefit is smaller and the long-term safety is unknown. For pregnant women, the preterm birth signal is a reason to pause. For older adults, the vaccines work for one season but the GBS signal and waning efficacy mean the net benefit is not as clean as advertised. Confidence: moderate for the monoclonal antibodies in high-risk infants, low for the maternal vaccine, low for the adult vaccines given the thin safety surveillance.