🫀 RSV Vaccines
3 major studies graded on 9 RCT methodology criteria.
RSV vaccines for older adults are the newest additions to routine adult vaccine schedules, all approved in 2023–2024. Three options entered the market: Arexvy (GSK), Abrysvo (Pfizer), and mRESVIA (Moderna's mRNA option). Because these vaccines are new, long-term follow-up is limited to one or two RSV seasons. Trials were large and well-designed by other measures.
🧪 What do these 9 criteria mean? click to expand
A comparison group received a different treatment (or no treatment) under identical conditions.
Without a control group, you cannot determine whether changes in outcomes were caused by the vaccine or other factors.
Participants were randomly assigned to vaccine or control — not by age, risk, or researcher choice.
Randomization prevents selection bias, ensuring the vaccinated and unvaccinated groups are comparable at baseline.
Neither participants nor researchers measuring outcomes knew who received the vaccine.
Blinding prevents both reporting bias (participants feeling better just from getting a shot) and measurement bias.
The control group received an inert substance (saline) — not another active vaccine.
Active comparators can mask safety signals. If the control group also experiences side effects, adverse events in the test group may appear deceptively normal.
At least 1,000 participants were enrolled.
Larger samples detect modest effects and rare adverse events. A 200-person study might miss a side effect affecting 1 in 500.
Participants were tracked for at least one year after vaccination.
Short follow-up windows miss delayed adverse events, waning immunity, and long-term effectiveness.
Funded primarily by government, universities, or non-profits — not the manufacturer.
Industry-funded trials are statistically more likely to show positive results for the funder's product. This is a documented pattern, not an accusation.
Published in a peer-reviewed journal after independent scientific review.
Peer review catches methodological errors, though it is not a guarantee of correctness.
Independent researchers or real-world surveillance data confirmed the core findings.
Single trials can contain errors. When multiple independent studies find similar results, confidence increases substantially.
Study Summary
Phase 3 trial of Arexvy (adjuvanted RSV prefusion protein vaccine) in 24,966 adults aged 60+. Reported 82.6% efficacy against RSV lower respiratory tract disease over one RSV season. First RSV vaccine for older adults approved in the US (FDA: May 2023). Second-season data shows persistent but reduced efficacy.
Strengths
Large, rigorous, placebo-controlled, double-blind, multinational. Saline placebo. Results confirmed in second RSV season data and emerging real-world surveillance.
Limitations
One RSV season follow-up (~6 months). Cannot determine duration of immunity. Entirely GSK-funded. Rare cases of Guillain-Barré syndrome have been reported post-approval; causality under investigation.
Study Summary
Phase 3 trial of Abrysvo (unadjuvanted bivalent RSV prefusion protein vaccine) in 34,284 adults aged 60+ — the largest of the three RSV trials. Reported 66.7% efficacy against RSV lower respiratory tract disease. FDA approved June 2023. Also approved for use in pregnancy to protect newborns.
Strengths
Largest RSV trial by enrollment. Randomized, double-blind, placebo-controlled. Published in NEJM. Confirms vaccine class efficacy independently.
Limitations
Entirely Pfizer-funded. Single RSV season only. Efficacy (66.7%) lower than Arexvy (82.6%) — though direct comparison is confounded by different seasons and populations. Second-season data pending.
Study Summary
Phase 3 trial of mRESVIA (Moderna's mRNA RSV vaccine) in 35,541 adults aged 60+. Reported 83.7% efficacy against RSV lower respiratory tract disease. FDA approved May 2024 — the first mRNA vaccine for any indication other than COVID-19. Primary analysis covered ~3.5 months of follow-up.
Strengths
Very large sample. Randomized, double-blind, placebo-controlled. Published in Lancet. Demonstrates mRNA platform efficacy for RSV, expanding its validation beyond COVID-19.
Limitations
Shortest follow-up of the three RSV trials (~3.5 months). Entirely Moderna-funded. Newest vaccine — real-world effectiveness data most limited. More frequent injection site reactions than placebo.
📋 What This Means
All three RSV vaccines met the core RCT requirements: large, randomized, double-blind, placebo-controlled. The consistent limitation is short follow-up — one RSV season (~3–6 months). We don't yet know how long protection lasts in 60–80 year olds. All trials were manufacturer-funded. Second-season data is emerging, showing waning but persistent protection. Rare post-marketing safety signals (e.g., possible Guillain-Barré link) are under active monitoring.