Why hepatitis B immunization requires a series of injections

The first injection introduces the immune system to hepatitis B. Later doses reinforce that response, helping the body recognise the virus more effectively. The exact timing depends on age, health, previous vaccination, and whether there has been a recent exposure.

A delayed dose does not usually mean the whole course must start again. A clinician can check the record and arrange the next dose. Vaccination prevents infection; it does not treat an infection already present. Learn more about [Hepatitis B](/conditions/hepatitis-b/).

Keep a written or digital record of every injection and ask the vaccination service when the next one is due. Tell the clinician about pregnancy, immune problems, serious illness, or a previous reaction to a vaccine. Attend the appointment even if you feel well, because hepatitis B may cause few early symptoms.

If you develop dark urine or unusual tiredness, arrange medical assessment rather than assuming it is a vaccine effect. A [Liver Function Test](/treatments/diagnostics-and-screening/liver-function-test/) may be part of an evaluation.

Seek urgent care for trouble breathing, swelling of the face or throat, fainting, or widespread hives after an injection. Contact a clinician promptly for yellowing of the eyes, persistent vomiting, severe abdominal pain, marked weakness, or confusion. These symptoms need assessment and are not a reason to abandon future doses without medical advice.

Ask which schedule applies to you, what to do after a missed appointment, whether testing is appropriate, and how your other medicines or health conditions affect vaccination.