AstraZeneca has entered into a definitive agreement to acquire Icosavax Inc, a US-based clinical-stage biopharmaceutical company focused on developing differentiated, high-potential vaccines using an innovative, protein virus-like particle (VLP) platform.

The proposed acquisition will build on AstraZeneca’s expertise in respiratory syncytial virus (RSV), strengthening AstraZeneca’s Vaccines & Immune Therapies late-stage pipeline with Icosavax’s lead investigational vaccine candidate, IVX-A12. IVX-A12 is a potential first-in- class, Phase III-ready, combination protein VLP vaccine which targets both RSV and human metapneumovirus (hMPV), two leading causes of severe respiratory infection and hospitalization in adults 60 years of age and older and those with chronic conditions such as cardiovascular, renal and respiratory disease.1-3 There are currently no treatments or preventative therapies for hMPV and no combination vaccines for RSV.4

IVX-A12 is the most advanced investigational vaccine targeting both RSV and hMPV and has a differentiated profile versus currently approved RSV vaccines. Phase II data demonstrate that IVX-A12 elicits robust immune responses against both RSV and hMPV one month after vaccination and reconfirm previous immunogenicity data seen in the Phase I trial.5

As VLP vaccines mimic how naturally occurring viruses appear to the body’s immune system, they may offer potential benefits over non-VLP vaccines, including a stronger immune response, greater breadth of protection, greater durability requiring fewer boosters and, compared to the current adjuvanted RSV vaccine, a lower incidence of side effects.6

Alongside Icosavax’s proprietary technology and leadership in protein design, the acquisition is expected to also bring their expertise and capabilities in protein virus-like particle science and development to AstraZeneca to support the progression of IVX-A12 and other differentiated VLP vaccines for high-burden respiratory infections.

Iskra Reic, Executive Vice President, Vaccines & Immune Therapies, AstraZeneca, said: “This virus-like particle vaccine technology has the potential to transform prevention against severe infectious diseases, including RSV and hMPV. With the addition of Icosavax’s Phase III-ready lead asset to our late-stage pipeline, we will have a differentiated, advanced investigational vaccine, and a platform for further development of combination vaccines against respiratory viruses. This aligns with our strategy to deliver a portfolio of therapies to address high unmet needs in infectious diseases, and our ambition to protect the most vulnerable patients who have high risk of severe outcomes.”

Adam Simpson, Chief Executive officer, Icosavax, said: “We are pleased to announce the proposed acquisition of Icosavax by AstraZeneca as we believe it offers the opportunity to accelerate, and expand access to, our potential first-in-class combination vaccine for older adults at risk of RSV and hMPV. We look forward to combining our skills and expertise in advancing the development of IVX-A12 with AstraZeneca’s decades of experience in RSV, resources, and capabilities in late-stage development.”

Under the terms of the agreement, AstraZeneca, through a subsidiary, will initiate a tender offer to acquire all of Icosavax’s outstanding shares for a price of $15.00 per share in cash at closing, plus a non-tradable contingent value right for up to $5.00 per share in cash payable upon achievement of a specified regulatory milestone and a sales milestone. The upfront cash portion of the consideration represents a transaction value of approximately $0.8bn, a 43% premium to Icosavax’s closing market price on 11th December 2023 and a 73% premium to the 60-day volume-weighted average price (VWAP) of $8.68 before this announcement. Combined, the upfront and maximum potential contingent value payments represent, if achieved, a transaction value of approximately $1.1bn, a 91% premium to Icosavax’s closing market price on 11th December 2023 and a 130% premium to the 60-day VWAP. As part of the transaction, AstraZeneca will acquire the cash and marketable securities on Icosavax’s balance sheet, which totaled $229m as of 30th September 2023.

RSV and hMPV in Older Adults

RSV is a common, contagious virus that is a major cause of lower respiratory tract infection in adults.7 Most adult RSV disease cases occur among older adults, with an estimated 60,000-160,000 hospitalizations and 6,000-10,000 deaths annually among US adults >65 years.8 RSV infection can cause serious complications such as pneumonia or exacerbation of congestive heart failure, asthma, and chronic obstructive pulmonary disease.7

hMPV causes disease very similar to RSV, including upper and lower respiratory tract infections that can be more severe in young children, older adults, and people with weakened immune systems.4 Adults with hMPV infection may have viral pneumonia, worsening asthma, or COPD symptoms.9 Data support similar morbidity and mortality for hMPV and RSV.2 There are currently no treatment or prevention options for hMPV.4


IVX-A12 is a liquid, refrigerator-stable formulation comprised of IVX-121, Icosavax’s RSV prefusion F protein VLP vaccine candidate, and IVX-241, Icosavax’s hMPV prefusion F protein VLP vaccine candidate.

In Icosavax’s Phase II trial, IVX-A12 showed robust immune responses across RSV and hMPV antibodies, reconfirming previous immunogenicity data seen in the smaller Phase I trial. The data are the first to demonstrate hMPV immune response in a Phase II combination vaccine trial.  IVX-A12 was generally well-tolerated in the trial, with a safety profile similar to that seen in the Phase I trial.5

IVX-A12 has been granted Fast Track Designation from the US Food and Drug Administration, a program designed to facilitate the development and expedite the review of investigational drugs to treat serious conditions and fulfill an unmet medical need.10