What's Actually Changed With the COVID Vaccine Since 2020

Ask someone what they think about the COVID vaccine and the answer is often shaped by 2020 or 2021 — the initial rollout, the mass vaccination programme, and the arguments that came with both.

Five years on, four separate things have changed: what the vaccine targets, how updates are approved, what products exist and — in Britain particularly — who it's actually being offered to.

That doesn't make the history irrelevant. But it does mean that "the COVID vaccine" in 2026 isn't quite the same proposition people were arguing about five years ago.

TL;DR

• The viral target has changed repeatedly. US vaccines have progressed from the ancestral strain through bivalent formulations, XBB.1.5, KP.2, LP.8.1 and now XFG for 2026–27.
• XFG has reached the UK too. UKHSA's August 2026 vaccine update lists Pfizer's XFG-adapted COMIRNATY as currently available in the UK, although US and UK authorisation and procurement remain separate processes.
• Annual strain changes don't restart vaccine development from Phase 1. Regulators rely heavily on accumulated evidence for the established vaccine platform, supplemented by evidence specific to the updated formulation. Exact requirements vary by vaccine and regulator.
• The products themselves have diversified. Moderna's mNEXSPIKE uses a different mRNA design from Spikevax, encoding two regions of spike rather than the full-length protein. Novavax's Nuvaxovid isn't an mRNA vaccine at all.
• Perhaps the biggest UK change is who the vaccine is for. England's autumn 2026 programme covers adults 75 and over, older-adult care-home residents and immunosuppressed people aged 6 months and over — a targeted programme rather than the population-wide offer seen earlier in the pandemic.
• A major JAMA evidence review published on 2 September 2026 found no new safety signals in recently published evidence. That's not the same as no known risks: myocarditis and pericarditis after mRNA vaccination, particularly in younger males, remain established concerns reflected in regulatory warnings.
• The same review exposed substantial limitations in the observational evidence. Of 84 comparative observational studies, only 3 were judged at low risk of bias and 50 at critical risk, primarily because of potential residual or uncontrolled confounding.

The Target Has Changed Repeatedly

The vaccines authorised at the end of 2020 were designed against the ancestral SARS-CoV-2 spike protein — the version of the virus sequenced near the beginning of the pandemic. That version stopped circulating meaningfully years ago.

As SARS-CoV-2 evolved, vaccine composition changed with it. In the US, the mRNA vaccines progressed from the original ancestral formulation to ancestral/BA.4–BA.5 bivalent vaccines, then XBB.1.5, KP.2, LP.8.1 and now XFG for the 2026–27 season. The FDA's 2026 strain-selection process recommended a monovalent JN.1-lineage vaccine using XFG, with XFG-adapted products subsequently approved for the new season.

Notably, the different vaccine manufacturers haven't always moved in perfect lockstep. Novavax, for example, used JN.1 for its 2024–25 and 2025–26 formulations while the US mRNA products used KP.2 and LP.8.1 respectively. That's an important reminder that even the phrase "the COVID vaccine" can obscure meaningful differences between products.

The basic principle, however, is straightforward: vaccines designed for a virus circulating in 2020 have progressively been replaced by formulations better matched to later SARS-CoV-2 lineages.

What About the UK?

For British readers, there's an important distinction between the FDA deciding what US vaccines should contain and what is actually available through the UK programme. Those are separate regulatory and procurement systems.

But XFG has now reached Britain too. UKHSA's August 2026 vaccine update lists Pfizer's XFG-adapted COMIRNATY as currently available in the UK. That doesn't mean every US vaccine decision automatically applies here, or that every COVID vaccine available in Britain must necessarily use precisely the same formulation. It does mean that XFG is now part of the UK vaccine landscape as well as the US one.

Recent UK sequencing has continued to identify a mixture of JN.1-descendant lineages, including XFG and its descendants. But with relatively few samples available for sequencing in some recent reporting periods, individual percentages can move sharply and shouldn't be overinterpreted.

The broader point is more durable: the ancestral and ancestral/Omicron bivalent formulations used earlier in the pandemic have been superseded by later variant-adapted vaccines.

How Annual Updates Are Approved

This is where a lot of confusion sits.

The original vaccines went through the full clinical development process, including large Phase 3 trials involving tens of thousands of participants. That established evidence for the vaccine platforms themselves. Updating the strain encoded in an established vaccine doesn't mean starting that entire development programme again from Phase 1.

Instead, regulators can draw on the accumulated clinical, safety and real-world evidence for the established vaccine while assessing evidence specific to the updated formulation. Depending on the product and regulator, that can include manufacturing and quality information, non-clinical studies and clinical or immunogenicity evidence.

For the 2026 XFG version of COMIRNATY, for example, Pfizer described the FDA decision as drawing on the accumulated clinical, non-clinical and real-world evidence for COMIRNATY alongside manufacturing, quality and non-clinical information specific to the XFG-adapted formulation. European regulatory guidance similarly allows evidence requirements for adapted COVID vaccines to depend on the nature of the change and the evidence already established for the parent vaccine.

So it isn't accurate to say every annual update undergoes another enormous Phase 3 efficacy trial. But it also isn't accurate to say an updated vaccine simply has its sequence changed without regulatory evaluation.

The principle resembles seasonal influenza vaccination: once a vaccine platform is established, its antigenic composition can be updated without recreating the original development programme every year. The regulatory frameworks for flu and COVID vaccines aren't identical, however. If you're weighing up winter respiratory illness more broadly, our guide to protecting yourself through a heavy flu winter covers the wider picture.

The Products Have Changed Too

Not every change since 2020 is simply a different viral sequence inside the same vaccine. The product landscape itself has evolved.

mNEXSPIKE. Moderna's mNEXSPIKE represents a genuine change in mRNA vaccine design. Spikevax uses mRNA encoding full-length spike protein. mNEXSPIKE instead encodes the spike protein's N-terminal domain and receptor-binding domain — two immunologically important regions — rather than the entire spike protein. Its current XFG formulation contains 10 micrograms of mRNA.

Importantly, mNEXSPIKE itself was independently clinically evaluated before approval. The vaccine was originally approved by the FDA in 2025; the 2026 XFG version is the subsequent seasonal strain update of that newer platform. So there are two different kinds of change here. Creating mNEXSPIKE was a change in vaccine design. Updating mNEXSPIKE from one variant target to XFG is a seasonal antigen update. Those aren't the same regulatory or scientific proposition.

Nuvaxovid. Nuvaxovid, made by Novavax, is different again. It isn't an mRNA vaccine. It's a protein-subunit vaccine containing recombinant SARS-CoV-2 spike protein together with the Matrix-M adjuvant, which enhances the immune response. The current US 2026–27 formulation uses recombinant XFG spike protein.

So the shorthand that "the technology is the same, only the target has changed" is broadly useful when comparing successive versions of established mRNA products, but it's incomplete as a description of the wider vaccine landscape. There are now different vaccine technologies and different mRNA designs, as well as different variant targets.

Perhaps the Biggest Change: Who the Vaccine Is For

For a British audience, this may be the most consequential change of all.

England's autumn 2026 COVID vaccination programme covers:

• Adults aged 75 and over
• Residents of care homes for older adults
• People aged 6 months and over who are immunosuppressed

That's fundamentally different from the population-wide vaccination offers seen earlier in the pandemic. JCVI is explicit about the current objective: vaccination is being targeted towards preventing serious disease — particularly hospitalisation and mortality — among people at greatest risk.

That changes the context in which the vaccine is being offered. For most people in Britain, the current question isn't whether they should routinely receive another COVID vaccination. They aren't eligible for one. The programme is increasingly a targeted intervention aimed at groups in whom the potential benefit from preventing severe COVID is greatest.

Anyone whose view of COVID vaccination formed during the universal-offer era is therefore, in a meaningful sense, evaluating a public-health policy that no longer exists.

What Does the Current Evidence Actually Show?

A major evidence review published in JAMA on 2 September 2026 provides one of the most comprehensive recent attempts to answer that question. Researchers screened 11,829 records and ultimately included 155 publications:

• 15 randomised controlled trials
• 84 comparative observational studies
• 38 uncontrolled product-safety studies
• 18 disease-burden studies

Its broad conclusion was that the newly reviewed evidence identified no new safety signals and that updated COVID vaccines continued to be associated with lower risk of hospitalisation. Both parts of that conclusion require context.

"No New Safety Signals" Doesn't Mean "No Known Risks"

This distinction matters.

Myocarditis and pericarditis following mRNA COVID vaccination are already recognised safety concerns, particularly among younger males. In June 2025, the FDA required updated warning information for mRNA COVID vaccines concerning myocarditis and pericarditis, noting that the observed risk had been highest among males aged 12 to 24.

So when the 2026 JAMA review says the newer evidence revealed no new safety concerns, it isn't claiming that vaccination has never been associated with adverse events. It means the evidence reviewed didn't reveal an additional safety signal beyond the risks already being monitored. The review itself discusses evidence of increased myocarditis risk in some younger populations following earlier vaccination.

There is also an important limitation around dosing intervals. The review noted that identified studies conducted under updated dosing guidance didn't report an increased myocarditis or pericarditis risk. But the eligible myocarditis studies largely involved vaccination before the February 2022 change in recommended dosing intervals. That's a considerably narrower conclusion than saying longer intervals have definitively eliminated the risk.

The Evidence Base Is Large — But Uneven

Another important finding received considerably less attention than the headline safety conclusion. Of the 84 comparative observational studies included in the JAMA review:

• 3 were judged at low risk of bias
• 11 at moderate risk
• 20 at serious risk
• 50 at critical risk

The authors said critical ratings were primarily driven by potential residual or uncontrolled confounding. That needs interpreting carefully. Under the review's prespecified criteria, observational studies failing to control for all three key confounders — age, season and immunocompromised status — were classified as being at critical risk of bias.

So "critical" doesn't mean researchers fabricated results or that the studies contain no useful information. It means their design leaves enough potential for important differences between vaccinated and comparison groups that causal interpretation becomes substantially less secure.

This matters because observational vaccine-effectiveness research is inherently difficult. People who choose or are eligible to receive a vaccine can differ from those who don't in age, health, healthcare use, previous infection, socioeconomic circumstances and other ways. Statistical adjustment can reduce that problem. It can't always remove it. It's the same interpretive problem that runs through much of the observational evidence on inflammation and diet.

How Effective Are the Updated Vaccines?

The same JAMA review found continuing protection against severe outcomes, particularly in older adults. For adults aged 65 and over, one study of the 2025–26 updated vaccine estimated 53% effectiveness against COVID-related hospitalisation. Across eight observational studies of JN.1-lineage-updated vaccines in older adults, estimates against COVID-related hospitalisation ranged from approximately 35% to 59.3%.

UK surveillance from the previous autumn vaccination programme also found that recipients were around 43% less likely to be admitted to hospital with COVID from two weeks after vaccination compared with those who remained unvaccinated.

But there's an important chronological distinction. Those figures don't tell us the real-world effectiveness of the newly updated XFG vaccine. The XFG-adapted vaccines have only just entered use. There isn't yet real-world effectiveness evidence for the new XFG formulation.

Any precise claim about how well this season's XFG vaccine will prevent hospitalisation therefore involves extrapolation from previous formulations, immunological and non-clinical evidence, rather than direct real-world effectiveness data from the 2026–27 season. That evidence will accumulate as the season progresses.

What This Actually Means

The COVID vaccine has changed since 2020 — but not in one simple way.

• The viral target has changed repeatedly as SARS-CoV-2 has evolved.
• The regulatory model now allows established vaccine platforms to be adapted without restarting their original clinical-development programmes.
• The product landscape has diversified, including different mRNA designs and protein-based vaccines.
• The British vaccination programme has moved from broad population vaccination towards targeted protection of people at greatest risk of severe disease.
• US and UK decisions aren't interchangeable. But XFG-adapted COMIRNATY is now available in the UK as well as XFG vaccines in the US.
• "No new safety signals" isn't the same as "no risks." Myocarditis and pericarditis following mRNA vaccination remain recognised adverse events, particularly in younger males.
• More evidence doesn't automatically mean better evidence. The recent JAMA review included 155 publications, but most comparative observational studies weren't judged to be at low risk of bias.
• And effectiveness figures need dates attached to them. Previous variant-adapted vaccines have shown protection against hospitalisation, but real-world effectiveness for the new XFG formulation hasn't yet been established.

Whatever the programme looks like this winter, the everyday foundations still matter — sleep, movement and recovery all shape how well you handle a winter respiratory season. Our Sleep Reset guide and Reset Companion can help you keep those steady when the days shorten.

Frequently Asked Questions

Is the COVID vaccine the same as it was in 2020? No. The viral target has been updated repeatedly as SARS-CoV-2 has evolved. Earlier ancestral and bivalent formulations have been superseded, while newer vaccine designs and non-mRNA options also exist.

What variant does this season's vaccine target? In the US, 2026–27 vaccines have been updated to target XFG. XFG-adapted Pfizer COMIRNATY is also currently available in the UK, although US and UK vaccine authorisation and procurement remain separate.

Do updated COVID vaccines go through clinical trials? The original vaccines went through full clinical-development programmes including large Phase 3 trials. Annual strain updates don't repeat that entire process from scratch. Regulators draw on existing evidence for the established vaccine plus evidence specific to the updated formulation. Exactly what new evidence is required varies by vaccine, type of update and regulator.

Who is eligible for the COVID vaccine in England this autumn? The autumn 2026 programme covers adults aged 75 and over, residents of care homes for older adults, and people aged 6 months and over who are immunosuppressed.

Does the COVID vaccine cause myocarditis? Myocarditis and pericarditis following mRNA COVID vaccination are recognised rare adverse events, with the observed risk highest in younger males. FDA labelling was updated again in 2025 to reflect this risk.

Did the latest research find the vaccines are completely safe? No study can establish that a medical intervention is "completely safe". The September 2026 JAMA review found no new safety signals in the evidence it examined. Existing recognised adverse effects, including myocarditis and pericarditis following mRNA vaccination, remain part of the safety profile.

How effective is the current XFG vaccine? We don't yet have real-world effectiveness estimates for the new XFG-adapted vaccine. Previous JN.1-lineage-updated vaccines were associated with reduced COVID-related hospitalisation, but those numbers shouldn't simply be presented as effectiveness estimates for XFG.

What is mNEXSPIKE? mNEXSPIKE is Moderna's newer mRNA COVID vaccine design. Rather than encoding full-length spike protein like Spikevax, it encodes the N-terminal and receptor-binding domains. The vaccine itself underwent clinical evaluation before approval; its current XFG formulation is a subsequent seasonal update of that platform.

Is there a COVID vaccine that doesn't use mRNA? Yes. Novavax's Nuvaxovid is a protein-subunit vaccine containing recombinant SARS-CoV-2 spike protein together with the Matrix-M adjuvant. Availability and eligibility depend on the country and current vaccination programme.

The Bottom Line

Four things have changed since 2020, and only one of them usually gets much attention.

The target has changed as SARS-CoV-2 has evolved. The regulatory approach has moved from establishing entirely new vaccines towards updating platforms with substantial accumulated evidence behind them. The products have diversified, including newer mRNA designs and protein-subunit alternatives. And in Britain, the programme itself has changed from broad population vaccination to targeted protection of people at greatest risk of severe disease.

The latest comprehensive evidence review found no new safety signals and continued evidence of protection against hospitalisation. But it also highlighted substantial limitations in much of the observational evidence, while established adverse effects such as myocarditis in younger males remain recognised. And for the newly introduced XFG vaccine, real-world effectiveness evidence doesn't exist yet.

None of this tells an individual whether they should be vaccinated. It does mean that a position formed five years ago — positive or negative — was formed around a different viral target, a different range of products, a different evidence base and, particularly in Britain, a very different vaccination programme.

Understanding what's changed doesn't require taking a side. It requires being precise about what is actually being offered now.

This is general information rather than medical advice. If you have questions about whether COVID vaccination is appropriate for you, particularly alongside existing health conditions, speak to your GP or another qualified healthcare professional.

Related reading

• The UK Super Flu Winter: How to Protect Yourself
• Travel Health Vaccinations: A UK Guide for 2026
• Measles in London Schools: Outbreaks, Vaccines and Protection
• Why Inflammation Rises in Winter

Popular Articles