H5N1 vaccine

Influenza A subtype H5N1

Influenza A virus subtype H5N1 Genetic structure Infection Human mortality Global spread in 2004 in 2005 in 2006 in 2007 2020–2025 Social impact Pandemic Vaccine

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A H5N1 vaccine is an influenza vaccine intended to provide immunization to influenza A virus subtype H5N1.

Vaccination of poultry against the avian H5N1 influenza epizootic is widespread in certain countries.^[6][7] Some vaccines also exist for use in humans, and others are in testing. As of July 2024 these include Aflunov, Celldemic and Seqirus/Audenz.^[8][9]

The hemagglutinin protein is the main viral antigen of influenza A viruses, including the H5N1 subtype. Vaccination can induce antibodies that block the functions of the H5 hemagglutinin and neutralize virus infectivity.^[10]

The influenza virus is highly variable - the H5N1 virus now infecting cattle in the USA^[a] is different from the H5N1 viruses that first showed up in poultry in 1997 and subsequently spread through wild bird populations in all continents except Australia. Scott Hensley, Professor of Microbiology at Perelman School of Medicine, has stated “If this H5 causes a pandemic, it likely is not going to be identical to whatever is circulating in cows [currently].” This means that any vaccine developed in anticipation of a human pandemic is unlikely to be an exact match to the pandemic strain.^[11] However licensed vaccines can be updated in a process similar to that used for updating seasonal influenza vaccines.^[12]

In December 2024 the UK government announced the purchase of five million doses of human H5 influenza vaccine to boost the country’s resilience in the event of a possible H5 influenza pandemic. The vaccine will be manufactured by CSL Seqirus UK Limited.^[13] The vaccine is based on the A/H5N8/Astrakhan/3212/2020 clade 2.3.4.4b strain of influenza.^[14] If needed, the H5 vaccine could be used while a pandemic-specific vaccine is developed and produced.^[15]

In July 2024, CSL Seqirus, Sanofi and GSK have collectively secured $72 million in funding from the U.S. health department to boost the country’s supply of bird flu vaccines.^[16]

In June 2024, the European Commission's Health Emergency Preparedness and Response Authority (HERA) signed a four-year contract with CSL Seqirus to secure 665,000 pre-pandemic vaccines with a provision for a further 40 million doses of avian flu vaccines. The member states participating in the contract are 15 of the 36 countries that have signed the EU's Joint Procurement Agreement for Medical Countermeasures, which includes all EU and EEA Member States. These fifteen countries^[17][18] are: Denmark, Latvia, France, Cyprus, Lithuania, Malta, the Netherlands, Austria, Portugal, Slovenia, Finland, Greece, Ireland, Iceland, and Norway.^[17]

In May 2024, CSL Seqirus was selected by the US government to supply 4.8 million doses of an H5 vaccine to the National Pre-Pandemic Influenza Vaccine Stockpile program. The vaccine is well matched to the H5N1 strains currently circulating in wild birds and cattle.^[19]

In January 2020, the U.S. Food and Drug Administration (FDA) approved Audenz, an adjuvanted influenza A (H5N1) monovalent vaccine.^[2][20] Audenz is a vaccine indicated for active immunization for the prevention of disease caused by the influenza strain which is contained in the vaccine (currently A/turkey/Turkey/1/2005 NIBRG-23).^[21] In the event of an outbreak of the disease in humans, the strain could be updated in a process similar to that used for updating seasonal vaccines.^[2][12]

In November 2013, the U.S. Food and Drug Administration (FDA) approved an experimental H5N1 bird flu vaccine to be held in stockpiles.^[22][23] In a clinical trial including 3,400 adults, 91% of people age 18–64 and 74% of people age 65 or older formed an immune response sufficient to provide protection. Reported adverse effects were generally mild, with pain at the injection site being the most common adverse effect.^[24]

A "candidate" vaccine is one which has been developed to be safe and effective, but has not yet received marketing authorisation.^[25] As of January 2025 the following vaccines are available or under development:

• Aflunov: A vaccine for adults and children over 6 months, approved for medical use in the European Union in November 2010. Aflunov contains the flu strain A/turkey/Turkey/1/2005 (H5N1)-like strain (NIBRG-23) (clade 2.2.1).^[26]
• Adjupanrix: approved for medical use in the European Union in October 2009. Adjupanrix contains the flu strain A/VietNam/1194/2004 NIBRG 14 (H5N1).^[27]
• Foclivia: approved for medical use in the European Union in October 2009. A vaccine that contains the A/Vietnam/1194/2004 (H5N1) flu strain.^[28]
• Pumarix: A vaccine approved for medical use in the European Union in March 2011.^[29]
• Seqirus/Audenz: A vaccine for adults that contains a killed flu strain called A/Astrakhan/3212/2020 (H5N8)-like strain.^[30]

Some older H5N1 vaccines for humans that have been licensed are:

• Sanofi Pasteur's vaccine approved by the United States in April 2007.^[31]
• GlaxoSmithKline's vaccine Prepandrix approved by the European Union in May 2008.^[32]
• CSL Limited's vaccine Panvax approved by Australia in June 2008.^[33]

H5N1 continually mutates, meaning vaccines based on current samples of avian H5N1 cannot be depended upon to work in the case of a future pandemic of H5N1. While there can be some cross-protection against related flu strains, the best protection would be from a vaccine specifically produced for any future pandemic flu virus strain. Daniel R. Lucey, co-director of the Biohazardous Threats and Emerging Diseases graduate program at Georgetown University, has made this point, "There is no H5N1 pandemic so there can be no pandemic vaccine."^[34] However, "pre-pandemic vaccines" have been created; are being refined and tested; and do have some promise both in furthering research and preparedness for the next pandemic.^[35] Vaccine manufacturing companies are being funded to increase flexible capacity so that if a pandemic vaccine is needed, facilities will be available for rapid production of large amounts of a vaccine specific to a new pandemic strain.^[36]

• Khurana S, Suguitan AL, Rivera Y, Simmons CP, Lanzavecchia A, Sallusto F, et al. (April 2009). "Antigenic fingerprinting of H5N1 avian influenza using convalescent sera and monoclonal antibodies reveals potential vaccine and diagnostic targets". PLoS Medicine. 6 (4): e1000049. doi:10.1371/journal.pmed.1000049. PMC 2661249. PMID 19381279.{{cite journal}}: CS1 maint: overridden setting (link)

• "Diagnostic Targets and Potential Vaccine Against H5n1 Avian Influenza". U.S. Food and Drug Administration (FDA). 21 October 2019.
• US patent 8778847, "Immunogenic peptides of influenza virus", published 2010-11-11, issued 2014-06-25 .
• "Pandemic Influenza". HHS.gov. 14 July 2016.