The One-Minute Jab

The NHS Begins the Switch

In May 2026, NHS England announced the rollout of a subcutaneous formulation of pembrolizumab, the checkpoint immunotherapy drug marketed by Merck as Keytruda. The new version, branded Keytruda Qlex, delivers the same active drug under the skin rather than into a vein. The injection takes between one and two minutes, depending on the dosing schedule. The intravenous infusion it replaces took up to two hours.

The change applies across all fourteen cancer types for which IV pembrolizumab was already approved: lung, breast, head and neck, cervical, endometrial, oesophageal, gastric, colorectal, kidney, bladder, liver, melanoma, Merkel cell carcinoma, and tumour-agnostic indications tied to specific biomarkers. About 14,000 patients begin pembrolizumab therapy in England each year. Most are expected to switch.

The regulatory path was rapid by pharmaceutical standards. The US Food and Drug Administration approved Keytruda Qlex in September 2025. The European Commission followed in November. The UK's Medicines and Healthcare products Regulatory Agency cleared it shortly after, opening the door for NHS commissioning in early 2026.

The practical knock-on effects are significant. IV pembrolizumab requires a hospital pharmacy team to prepare infusion bags under sterile conditions before each dose, a process that is labour-intensive and limits throughput. The pre-filled subcutaneous syringe skips that preparation entirely. Treatment chairs in infusion suites, which are scarce in most NHS trusts, turn over faster. Clinic schedules expand. And for a drug being given every three to six weeks as a long-term maintenance therapy, the aggregate time saving across a patient's full treatment course is measured in days.

Professor Peter Johnson, NHS National Clinical Director for Cancer, described the shift plainly: "This immunotherapy offers a lifeline for thousands of patients and it's fantastic that this new rapid jab can now take just a minute to deliver, meaning patients can get back to living their lives rather than spending hours in a hospital chair."

The Checkpoint That Cancer Learned to Pull

To understand why pembrolizumab matters, you need to understand a piece of immunological trickery that tumours have been using against us for decades without anyone knowing exactly how to stop it.

Your immune system runs on recognition and permission. T-cells patrol the body, checking the surfaces of cells they encounter. When a T-cell recognises something foreign or abnormal, it has the machinery to destroy it. But it also has an off-switch, a protein called PD-1 (Programmed Death-1) that sits on the T-cell's surface. When PD-1 latches onto a corresponding protein called PD-L1, which is displayed on normal healthy cells, the signal is clear: this cell is supposed to be here, stand down. The immune system doesn't eat its own tissues. The checkpoint is what prevents it from doing so.

Cancer cells discovered a catastrophic exploit. Many tumours produce large quantities of PD-L1. They wear the "healthy cell" disguise so aggressively that incoming T-cells, even ones that have correctly identified the abnormality, get shut down before they can act. The immune system has been recruited to protect the tumour.

Pembrolizumab blocks PD-1 on the T-cell side. It's a monoclonal antibody, a precisely engineered protein that latches onto PD-1 and physically prevents it from binding to PD-L1. The tumour can still wave its fake ID. The T-cell just stops caring. The checkpoint gets bypassed and the immune system attacks.

This is not a cure. It's worth being exact about that. Pembrolizumab produces durable responses in a meaningful fraction of patients, but response rates vary substantially by cancer type and by whether the tumour expresses PD-L1 at detectable levels. In non-small-cell lung cancer with high PD-L1 expression, the five-year survival rate with pembrolizumab as first-line therapy is around 31%, compared to roughly 16% with chemotherapy in comparable populations. In triple-negative breast cancer, adding pembrolizumab to neoadjuvant chemotherapy increased pathological complete response rates from about 40% to 54% in recent trial data. Some patients have lasted a decade on immunotherapy. Others progress within months.

The drug works best when the immune system already has T-cells that recognise the tumour, has been actively suppressed by the PD-L1 mechanism, and can be re-activated by lifting that suppression. Not every tumour creates that environment. The field is still learning which patients will respond and why.

Why It Took This Long to Make a Jab

Pembrolizumab has been FDA-approved since 2014. For a decade, it required IV infusion. That wasn't negligence or lack of ambition. It was physics.

Antibody drugs like pembrolizumab are large, complex proteins. The IV formulation delivers 200mg of drug dissolved in a 25mL solution directly into the bloodstream, where it disperses immediately. The subcutaneous space, the layer of fat and connective tissue just beneath the skin, operates under different rules. Injections into that space are limited to about 1.5 to 2mL of volume. Push beyond that and the injection becomes painful and the drug pools rather than dispersing. But 200mg of pembrolizumab can't be squeezed into 2mL at any concentration that remains physically stable.

The solution that unlocked subcutaneous delivery was berahyaluronidase alfa. This is a recombinant enzyme, a modified version of the naturally occurring human enzyme hyaluronidase PH20. In the body, hyaluronidase breaks down hyaluronic acid, a dense polysaccharide that forms a mesh in the subcutaneous extracellular matrix. That mesh is the reason large-volume injections under the skin don't work: the drug hits the matrix and stalls.

When berahyaluronidase is co-injected with pembrolizumab, it temporarily hydrolyses the hyaluronic acid network at the injection site. The mesh loosens. The drug can now disperse through a much larger volume of subcutaneous tissue and get absorbed into the lymphatic and vascular system. The enzyme's effect is local and transient: the matrix repairs itself within 24 to 48 hours. Nothing permanent happens.

The challenge was making this work with a high-concentration pembrolizumab formulation. The research team at Merck had to develop a stable liquid in which the antibody, at roughly ten times the concentration of the IV formulation, doesn't aggregate, degrade, or change its binding characteristics. Proteins at high concentration have a tendency to clump together, which destroys their function and creates immune responses in patients. Getting the excipient chemistry right, the buffers, stabilisers, and pH adjustments, required years of formulation science.

The pivotal Phase 3 trial, 3475A-D77, demonstrated that the subcutaneous formulation achieved non-inferior pharmacokinetics compared to the IV version. The drug's area-under-curve (a measure of total drug exposure) and peak concentration fell within the pre-specified equivalence margins. Clinically, the body sees essentially the same drug, in the same amounts, behaving in the same way. The FDA found this sufficient for approval without requiring new efficacy trials.

That decision has attracted some scrutiny. A 2026 commentary in the Journal of Clinical Oncology asked pointedly whether the reformulation represented a meaningful clinical advance or a regulatory strategy that extended market exclusivity while offering limited new evidence that patients actually benefit differently. The authors noted that SC formulations generate new patents, new delivery devices, and new pricing opportunities, often timed around the expiry of original compound protection.

Merck's position is that the convenience and throughput benefits are themselves clinically meaningful. The NHS appears to agree: the rollout is comprehensive, not selective. For the patients sitting in infusion chairs every three weeks, the debate over patent strategy is largely beside the point.

The Access Question Gets Louder

The NHS rollout is the part of this story that gets the headlines. But the more consequential version of this story is playing out in the 130 or so countries where IV pembrolizumab isn't reliably available in the first place.

Intravenous immunotherapy requires infrastructure: refrigerated pharmacy suites, trained chemotherapy nurses, infusion chairs, IV lines, monitoring equipment. In high-income countries, these are baseline hospital facilities. In much of sub-Saharan Africa, South Asia, and parts of Latin America and Southeast Asia, they're scarce or nonexistent outside major urban teaching hospitals. The treatment has been approved by regulators. But the regulatory approval of a drug and the ability of a health system to actually deliver it are different things entirely.

A subcutaneous injection changes that equation. The technical requirements drop sharply. A pre-filled syringe can be stored in a standard medical refrigerator and administered by a nurse without specialist oncology training. Community health centres, district hospitals, outpatient clinics, all become plausible delivery points. Patients who can't travel three hours to a tertiary centre every three weeks might be able to access treatment closer to home.

This is not yet a reality. Keytruda Qlex, like its IV predecessor, carries a price tag that makes it inaccessible in most low- and middle-income countries without substantial external support or negotiated tiered pricing. Pembrolizumab biosimilars, which could break the cost barrier, are in development but face their own approval timelines and manufacturing challenges.

There's a further complication that oncologists in lower-resource settings have raised directly. The IV formulation of pembrolizumab can be dosed by weight, which is clinically important: a small patient doesn't necessarily need the same amount of drug as a large one, and lower-dose regimens have shown comparable efficacy in some studies, making the drug go further per vial. The subcutaneous formulation delivers a fixed dose. That fixed-dose architecture works well in high-income systems where cost per dose is predetermined by procurement contracts. In lower-income settings, where stretched budgets depend on flexible dosing to treat more patients with the same supply, it's a step backward.

The global picture, then, is ambivalent. A drug that was already out of reach for most of the world's cancer patients has become more convenient for the fraction who had access to it. Whether the subcutaneous route eventually becomes a bridge toward broader access, rather than a premium add-on for existing high-income markets, depends on pricing decisions that will be made in board rooms, not clinics.

What isn't ambivalent is the science. Checkpoint immunotherapy is one of the genuine transformations in oncology of the last thirty years. Pembrolizumab is now approved for more indications than any drug in FDA history. The biology it exploits, the interplay between tumour immune evasion and T-cell surveillance, is still being mapped: researchers are actively combining pembrolizumab with targeted therapies, vaccines, and other checkpoint inhibitors to push response rates higher and extend durability in patients who currently progress.

The one-minute jab is a logistics story. The PD-1 pathway is a biology story. They're connected by the same drug, in the same pre-filled syringe, now sitting in a nurse's hand in a cancer clinic in England, ready to go in sixty seconds.

For the patient pulling their shirt back down, that's what changed. For the researchers still trying to make it work for everyone: there's more to do.