Pharmacology · Bacterial and antimalarial vaccines
Diphtheria vaccine (diphtheria toxoid) !
Inactivated diphtheria toxin that induces antitoxin antibodies. It is almost always combined with tetanus and pertussis (DTP, pentavalent, Td).
Updated 2026-11-01
Also called: Diphtheria toxoid, DTP / Td (combinations)
The figure shows monomeric diphtheria toxin from Corynebacterium diphtheriae; the vaccine contains this toxin in inactivated form (toxoid).
Mechanism of action
Diphtheria is a toxin-mediated disease: only strains infected by a bacteriophage carrying the toxin gene make toxin. The toxin inhibits protein synthesis, forms the pseudomembrane and damages the heart and nerves. The toxoid induces IgG that neutralises the toxin; it protects against disease although it does not fully stop carriage.
- Diphtheria toxoid is injected, almost always in a combination vaccine
- Antitoxin antibodies and memory form
- IgG neutralises the toxin before it enters cells
- No free toxin means no pseudomembrane, myocarditis or neuritis
Pharmacokinetics
- Onset and duration
- Protection needs the primary series and boosters to last
Indications
- Childhood series in combination vaccines with tetanus and pertussis
- Boosters in adolescents and adults (Td) and vaccination of diphtheria survivors during recovery
Adverse effects
Common
- Local pain and swelling
- Low-grade fever, irritability in children
Contraindications
- Previous anaphylaxis to a dose or a component
- For pertussis-containing combinations: encephalopathy with no other cause within seven days of a previous dose
Key interactions
- Diphtheria antitoxin
- Not mutually exclusive: a survivor treated with antitoxin starts or completes vaccination on recovery
What is monitored
- Vaccination series complete for age
- Local and systemic reactions after the dose
Administration and safety
- Intramuscular route
- Confirm the formulation (paediatric DTP or adult Td) for age, as they carry different amounts of toxoid
- Record the batch and product given
Nursing care
- Check the vaccination card before giving
- Ask about reactions to previous doses
- Watch for fever and local reaction, and teach the family the warning signs
Pregnancy and breastfeeding
Td can be used in pregnancy when the woman is not protected.
Test yourself
Think of the answer, then tap the question to see it.
Why do not all Corynebacterium diphtheriae strains cause severe diphtheria?
Only strains infected by a bacteriophage carrying the toxin gene produce toxin.
What are the most frequent complications of diphtheria?
Myocarditis and neuritis, caused by circulating toxin.
Why should a diphtheria survivor be vaccinated?
The disease does not always leave immunity; vaccination with toxoid is completed during recovery.
Related drugs
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Diphtheria (World Health Organization, 2026); Chapter 7: Diphtheria | Pink Book | CDC (Centers for Disease Control and Prevention, 2021); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); eEML - Electronic Essential Medicines List (World Health Organization, 2025).
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Representative model, for educational purposes only.