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Fact check: What do peer-reviewed studies published in 2022–2024 report for mRNA booster effectiveness against hospitalization from Omicron subvariants?
Executive Summary
Peer-reviewed and network studies from 2022–2024 consistently report that mRNA booster doses reduce risk of hospitalization from Omicron subvariants but the magnitude of protection varies by subvariant, vaccine formulation, and time since vaccination. Early post‑booster relative vaccine effectiveness (rVE) estimates cluster in the ~30–55% range against hospitalisation for newer Omicron sublineages (including BA.4/BA.5, XBB and XBB‑derivatives) but protection wanes over weeks to months, and effectiveness against some lineages (e.g., JN.1) appears lower than against XBB in the first 7–89 days after updated doses [1] [2] [3].
1. What the studies actually claim — concise extraction of key findings
Across the analyses provided, the central claims are consistent: mRNA boosters (both original and updated bivalent/monovalent formulations) reduce severe outcomes and hospitalisation from Omicron subvariants, but effect size and durability differ by variant and dose history. A UK study estimated incremental effectiveness of a BA.1 bivalent booster at 48.0% against BQ.1, 29.7% against CH.1.1, and 52.7% against XBB.1.5 at 5–9 weeks post‑vaccination [1]. Multiple analyses of Moderna’s mRNA‑1273 showed three doses gave high VE against BA.1 with slower waning, while protection against BA.2‑related subvariants waned more rapidly, and a fourth dose offered only moderate, short‑lived protection against several Omicron subvariants [4] [5].
2. Head‑to‑head: updated boosters versus older formulations — who fares better?
Studies of updated formulations indicate meaningful incremental protection when compared to no recent booster, but not full protection and with variation by lineage. A 2024 evaluation of the mRNA‑1273 BA.4/BA.5 bivalent vaccine reported rVE of 52.7% against BA.4/BA.5 and 48.8% against XBB at 14–60 days, with waning thereafter [2]. An IVY Network report of the 2023–2024 monovalent XBB.1.5 dose found 54.2% VE against XBB lineage hospitalization versus 32.7% against JN lineage during days 7–89 after the updated dose, showing updated monovalent formulations can outperform older boosters for some lineages but not uniformly [3].
3. Waning is real — timing matters for measured effectiveness
Multiple analyses establish a clear pattern: stronger protection shortly after boosting that declines over time. The Moderna-focused work reports three‑dose protection against BA.1 that wanes slowly, while effectiveness against BA.2 and its descendants waned more rapidly and a fourth dose produced only transient benefit [4]. The BA.4/BA.5 bivalent study explicitly documents higher rVE in the 14–60 day window with subsequent decline [2]. Systematic reviews and IVY Network analyses concur that durability is limited, with notable drops in VE by a few months post‑boost, and lower effectiveness against some emergent lineages like JN.1 [6] [7].
4. Dose number, product, and outcome definitions shift the numbers
Reported effectiveness varies with whether studies measure incremental rVE versus no recent booster, absolute VE, or protection after 3 versus 4 doses, and whether endpoints are infection, hospitalisation, or severe in‑hospital outcomes. The analyses show three doses provided substantial protection against BA.1 hospitalisation while additional doses offered incremental but shorter‑lived gains for other subvariants [4]. Studies of bivalent mRNA boosters report moderate incremental effectiveness against hospitalisation across several Omicron subvariants [1] [2], and IVY Network analyses place updated 2023–2024 vaccines in the moderate‑protection category for XBB but with lower performance for some JN lineages [3] [6].
5. Caveats, potential biases, and what’s missing from the picture
The evidence comes from observational and network hospital studies with heterogeneous designs, follow‑up windows, and comparator groups, which can influence rVE estimates. Some reports are preprints or limited‑sample network analyses and may not capture longer follow‑up or population heterogeneity [3] [8]. Studies emphasize short‑term rVE windows (e.g., 7–89 or 14–60 days), so longer‑term protection and effectiveness against evolving sublineages remain less precisely quantified. Public‑health agencies and manufacturers have incentives to highlight benefits of updated boosters; conversely, some study authors stress limitations in durability, which may temper policy interpretations [9] [7]. Overall, the consistent factual signal is moderate, variant‑dependent protection against hospitalization soon after mRNA boosting, with meaningful waning by months [1] [2] [3].