$115 million. That's what a London startup raised this week to pursue something vaccines haven't delivered: reliable, season-long flu protection from a single dose.
RQ Bio closed an oversubscribed Series A on June 24, led by Frazier Life Sciences, with EQT Life Sciences, Forbion, and Wellington Management joining. Its lead asset, RQB01, is a long-acting monoclonal antibody designed to prevent influenza in immunocompromised and high-risk patients — the population vaccines consistently fail to protect.
Long-acting antibodies will become a new standard for flu prophylaxis in vulnerable patients, starting with a $115M bet that RQB01 can prove it in the clinic.
Antibody-based prevention has been tried before. The economics of a biologic for seasonal use have never worked, and a single IND-enabling candidate is not evidence of a shift.
Why flu still wins
Seasonal influenza causes 3 to 5 million severe cases and up to 650,000 deaths per year globally, according to WHO data. The numbers have not moved meaningfully in a decade.
Vaccine effectiveness varies from 20% to 60% depending on the season. In immunocompromised patients (transplant recipients, people on chemotherapy, the elderly), seroprotection rates after vaccination can drop below 30%. These patients need something else.
Existing antivirals like oseltamivir reduce symptom duration by about a day when taken within 48 hours. They are not prevention. Palivizumab, the only monoclonal antibody approved for respiratory virus prophylaxis, is restricted to RSV in infants and requires monthly injections throughout the season.
That is the gap RQ Bio is targeting.
The global influenza prophylaxis market was valued at roughly $6 billion in 2025, with vaccines accounting for almost all of it. Even capturing 5% of the immunocompromised segment would represent a $300 million annual opportunity — enough to support a specialty biologic if manufacturing costs can be controlled.
The case for long-acting antibodies
RQB01 is designed with a dual mechanism of action targeting conserved epitopes on the influenza virus, regions that mutate slowly across seasons. If the preclinical data holds, it could neutralize multiple strains regardless of annual drift. That alone would solve the biggest weakness of seasonal vaccines: the yearly mismatch gamble.
The antibody is engineered for extended half-life. The goal is a single administration that provides protection for an entire flu season. A subcutaneous injection, given once before winter, replaces the annual shot that works in only half of those who receive it.
The chemistry supports the ambition. Monoclonal antibody half-life extension is a mature technology: Fc engineering produces molecules that circulate for three to six months. Several long-acting antibodies are already approved in other indications. The platform risk is low.
The company's backers are not small. Frazier Life Sciences led the round. Christian S. Schade, former CEO of Halda Therapeutics (acquired by Johnson & Johnson for $3.05 billion in December 2025), joined as Executive Chairman. The company was co-founded by scientists from the University of Oxford and LifeArc, the UK medical research charity that helped humanize Keytruda.
The syndicate and the science point in the same direction: this is a credible shot at an unmet need.
The problems with antibody prophylaxis
Monoclonal antibodies make exceptional drugs for chronic diseases with high per-patient value — oncology, autoimmune conditions, rare diseases. They have never worked economically for seasonal prevention.
Palivizumab is the closest analog. Approved in 1998 for RSV, it requires five monthly injections per season, costs roughly $3,000 per dose in the US, and is restricted to the narrowest high-risk population — premature infants. Despite 25 years on the market, it has never become a standard public health tool. The economics prevented scale.
RQB01 would face the same math. A long-acting biologic for flu would need to be priced competitively with a $20 vaccine. Even if aimed only at immunocompromised patients — a US population of roughly 7 million — the per-dose cost would need to be orders of magnitude lower than typical antibody therapeutics.
Manufacturing is another layer. Antibodies require mammalian cell culture, purification, cold chain distribution, and parenteral administration. Scaling that for seasonal use in a world that already produces 500 million flu vaccine doses annually is not a preclinical exercise.
And RQB01 is still in IND-enabling studies. It has not been tested in humans. The conserved epitope story is compelling in theory, but several broadly neutralizing antibodies against influenza have failed to translate from animal models to clinical efficacy. The field has a graveyard.
Influenza remains a serious and persistent threat for patients whose immune systems cannot rely on vaccination alone. Our vision is to develop a preventative therapy capable of delivering reliable protection for an entire flu season with a single administration.— Mike Westby, CEO, RQ Bio
That is the vision. Execution is where every flu antibody program before RQB01 has stopped.
What the data will decide
The candidate needs to clear three thresholds. First, a pharmacokinetic profile that confirms six months of protective serum levels from a single injection. Second, neutralizing titers against the major circulating strains — H1N1, H3N2, and at least one influenza B lineage — that meet or exceed what vaccination achieves in healthy adults. Third, a safety database sufficient for regulatory approval in a prophylactic indication, where the tolerance for adverse events is near zero.
Each of these is a standard biotech de-risking step. All three together, for a seasonal biologic target, is the reason the field has no approved products after 25 years of trying.
Phase 1 data for RQB01 — expected 2027 at current timelines
Partnership or licensing deal from a major vaccine manufacturer
Comparable long-acting antibody programs advancing into the clinic
FDA or EMA guidance on prophylaxis trial design for seasonal antibodies
The discussion around RQB01 is often framed as a competition: antibodies versus vaccines. That framing misses the point. Vaccines work through active immunity — they train the body to defend itself over weeks. Antibodies provide passive immunity — immediate protection that fades. The two modalities are complementary, not substitutable.
A patient who cannot mount a vaccine response still needs something. The question is whether $115 million and a clever antibody are enough to build a commercial product around that need.
The company is about to find out. The company plans to start clinical development next year. If RQB01 clears Phase 1, the debate shifts from theoretical to commercial. Efficacy data will settle what arguments cannot.