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Bordetella pertussis filamentous haemagglutinin (FHA) is a protein found on the surface of Bordetella pertussis, the bacterium that causes whooping cough (pertussis). The full name used in the registry is Bordetella pertussis filamentous haemagglutinin adsorbed on aluminium phosphate. It is not a medicine given on its own, but an antigen used as a component of acellular pertussis vaccines.
FHA is one of the purified antigens included in the authorised vaccine VacPertagen, where each 0.5 ml dose contains 5 micrograms of FHA adsorbed on hydrated aluminium hydroxide, alongside a genetically inactivated pertussis toxin (PTgen).[2] The same antigen is present in the combination vaccine Vaxelis, which also protects against diphtheria, tetanus, hepatitis B, poliomyelitis and Haemophilus influenzae type b.[1] FHA is also used in laboratory tests that measure antibodies against pertussis in blood samples.[3]
As a vaccine antigen, FHA is a purified part of the pertussis bacterium. When injected, it teaches the immune system to recognise the real bacterium. The body produces antibodies against FHA, so that if the vaccinated person later meets Bordetella pertussis, the immune system can respond quickly and prevent or reduce the severity of whooping cough.[2]
In the laboratory, FHA is produced by cultivating B. pertussis in a special culture medium, then purifying the protein by chromatography. This purified FHA is used to measure the amount of immunoglobulin G (IgG), IgA and IgM antibodies in the blood of people with pertussis, which helps diagnose the infection and study immune responses.[3]
FHA is given as part of a vaccine by intramuscular injection. The authorised product VacPertagen is a suspension for injection in a pre-filled syringe, with a single 0.5 ml dose containing 5 micrograms of FHA.[2] In the clinical trial, the vaccine Vaxelis was given as a 0.5 ml intramuscular injection, and the comparison vaccine Triaxis was given in the same way.[1] FHA is not given as a standalone product; it is always part of a combination vaccine.
One completed Phase 3 interventional trial, NCT05856396, enrolled 240 participants to study maternal determinants of infant immunity to pertussis.[1] The trial compared two vaccines: Vaxelis, which contains FHA among other antigens, and Triaxis, a reduced-antigen diphtheria, tetanus and acellular pertussis vaccine. Both were given as 0.5 ml intramuscular injections.[1]
The main objective was to identify key predictors of vaccine responses in pregnant women, of the transfer of maternal antibodies to the newborn, and of vaccine responses in infants. The primary outcome measured was the magnitude of the antibody responses to pertussis vaccination. The trial is now completed.[1]
The sources provided do not include detailed side effect information for FHA as a single component. The product information for VacPertagen notes that formaldehyde may be present in small amounts as a residue from the manufacturing process.[2] Side effects of pertussis-containing vaccines are generally assessed for the whole vaccine product rather than for FHA alone.
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