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This week’s deep dive
What’s Actually Changed With the COVID Vaccine
Ask most people what they think about the COVID vaccine and the answer is usually shaped by 2020 or 2021. Five years on, four separate things have changed — and only one of them gets much attention.
The target has changed repeatedly. The 2020 vaccines were designed against the ancestral SARS-CoV-2 spike protein, a version that stopped circulating meaningfully years ago. US vaccines have since moved through bivalent formulations, XBB.1.5, KP.2, LP.8.1 and now XFG for 2026–27. XFG-adapted Pfizer COMIRNATY is listed as currently available in the UK too, though UK and US authorisation remain separate processes.
The regulatory model has changed. Annual strain updates don’t restart development from Phase 1. Regulators draw on accumulated evidence for the established platform plus data specific to the updated formulation — manufacturing, quality, non-clinical and, where required, immunogenicity. It resembles the seasonal flu approach, though the frameworks aren’t identical.
The products have diversified. Moderna’s mNEXSPIKE encodes only two regions of the spike protein rather than the full-length version — a genuine design change, separately evaluated before approval. Novavax’s Nuvaxovid isn’t an mRNA vaccine at all.
And in Britain, the programme itself has changed. Autumn 2026 eligibility covers adults 75 and over, older-adult care home residents, and immunosuppressed people aged 6 months and over. That’s a targeted intervention, not the population-wide offer of 2021.
A major JAMA review published on 2 September found no new safety signals across 155 publications — while also being candid that only 3 of its 84 comparative observational studies were at low risk of bias, and that established concerns like myocarditis in younger males remain recognised in regulatory warnings.
None of that tells anyone what to do. It does mean a position formed five years ago was formed about a different vaccine, a different evidence base and a different programme.
Read the full piece →
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