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Diphtheria toxoid is a chemically inactivated form of the toxin produced by Corynebacterium diphtheriae, the bacterium that causes diphtheria. The toxoid retains the ability to trigger an immune response but cannot cause disease. In the CTIS product records linked to the trials below, the substance is registered as part of fixed combinations in four product records, with authorisations in Finland, the European Union, the Netherlands and the United Kingdom.[3] The authorisation holder is Sanofi Pasteur Europe.[3] The UK dm+d browser lists diphtheria toxoid as an ingredient in eleven virtual medicinal products, always in combination with other vaccine antigens such as tetanus, pertussis, polio, hepatitis B and Haemophilus influenzae type b.[6]
Diphtheria toxoid works by exposing the immune system to an inactivated version of the diphtheria toxin. This exposure prompts the body to produce specific antibodies against the toxin. If a vaccinated person later encounters the actual diphtheria bacterium, these antibodies can neutralise the toxin before it causes tissue damage. The same principle applies to the tetanus toxoid and pertussis toxoid components that commonly accompany diphtheria toxoid in combination vaccines.[6]
Diphtheria toxoid is given as an intramuscular injection, always as part of a combination vaccine. The pharmaceutical form recorded in the CTIS product records is a suspension for injection.[3] The UK dm+d browser lists several presentations, including 0.5 ml pre-filled syringes and vials, for products such as diphtheria/tetanus/pertussis/acellular component/poliomyelitis vaccines and diphtheria/tetanus/pertussis/acellular component/hepatitis B/poliomyelitis/Haemophilus type b conjugate vaccines.[6] The Milton Keynes formulary records diphtheria vaccines including Infanrix-IPV+Hib, Pediacel, Boostrix-IPV, Infanrix IPV, Repevax and Revaxis.[7] In the Humber and North Yorkshire formulary, the dTap/IPV vaccine Boostrix-IPV is noted as second line for pregnant women to protect their newborn from pertussis.[8]
Five trials are listed in the registry data, covering 1,285 participants. The trials span Phase 2, Phase 3 and Phase 4 and include completed studies as well as authorised studies not yet started or ongoing. One trial investigates diphtheria toxoid-containing vaccines as the test intervention, one uses them as a comparator, and one lists them as an auxiliary medicine.[3][2][5]
The Phase 3 trial in 100 healthcare workers (HC dTap) measured pertussis-specific IgG antibody concentrations before and four weeks after a booster with the Triaxis dTap vaccine. This trial is completed.[3] The Phase 3 MADI-02 trial in 240 participants examined how maternal vaccination during pregnancy influences antibody transfer to newborns and infant vaccine responses to pertussis; it is also completed.[4] The Phase 3 KIM study in 99 healthy adults tested whether a Tdap-IPV booster reduces colonisation with Bordetella pertussis after controlled human infection compared with a Td-IPV control; this trial is completed as well.[1]
The Phase 4 designation appears in the KIM study title, although the registry record lists it as Phase 3.[1] The Phase 2 trial in 750 infants, toddlers and children is authorised and investigates a pentavalent meningococcal ABCYW vaccine, with Hexyon — a diphtheria toxoid-containing hexavalent vaccine — serving as one of the comparator or co-administered vaccines.[2]
The trials enrolled different populations. The HC dTap trial recruited healthcare workers.[3] The MADI-02 trial enrolled pregnant women and their infants.[4] The MATIMMUNE trial, authorised and Phase 3, enrolled 96 pregnant women to study the timing of Tdap vaccination in pregnancy.[5] The KIM study enrolled healthy adults.[1] The Phase 2 meningococcal vaccine trial enrolled healthy children, toddlers and infants.[2]
The trials measure immune responses and, in some cases, clinical outcomes. The HC dTap trial measured the percentage of participants with pertussis toxin-specific IgG antibody geometric mean concentration (GMC) at or above 5 IU/mL before vaccination.[3] The MADI-02 trial measured the magnitude of antibody responses to pertussis vaccination in infants born to mothers immunised during pregnancy.[4] The MATIMMUNE trial measured antibody levels and functional antibody characteristics in maternal blood at baseline, after Tdap vaccination, at delivery and six months postpartum.[5] The KIM study measured Bordetella pertussis colonisation rates in nasal wash samples between day 3 and day 28 after challenge.[1] The Phase 2 meningococcal trial measured safety outcomes including solicited injection site reactions, systemic reactions, adverse events and serious adverse events, as well as meningococcal antibody titres using hSBA (serum bactericidal antibody) assays.[2]
The supplementary sources do not report specific side effect frequencies for diphtheria toxoid-containing vaccines. The Phase 2 meningococcal trial lists solicited injection site reactions, systemic reactions, unsolicited adverse events and serious adverse events among its measured outcomes, indicating that reactogenicity and safety are being formally assessed.[2] The NHS formularies referenced here do not provide side effect data for these products.[7][8]
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