Attenuated and inactivated vaccines: what to know

Attenuated vaccines use a weakened living organism, while inactivated vaccines use killed organisms or components that cannot reproduce. Both train the immune system to recognise a specific infection, but their handling, dose schedules and suitability can differ. The appropriate choice depends on the vaccine, your age, health, pregnancy status, medicines and previous reactions.

A live attenuated vaccine contains a version of the organism weakened so that it stimulates immunity without causing the usual illness in people for whom it is suitable. Because it can still replicate to a limited extent, it may be unsuitable during pregnancy or for someone with significant immune suppression.

An inactivated vaccine contains organisms that have been killed, or selected parts of them. These materials cannot multiply or cause the infection they protect against. Some inactivated vaccines need several doses or later boosters to build and maintain protection.

Before vaccination, tell the clinician if you are pregnant, have a weakened immune system, take medicines that suppress immunity, recently received another vaccine, or have had a serious allergic reaction to a vaccine or one of its ingredients. Bring your vaccination record so the clinician can check timing and avoid unnecessary repeat doses.

After vaccination, follow the clinic's instructions and keep the updated record. Soreness, redness, tiredness or a mild fever can occur as the immune system responds. Rest, drink fluids and ask a pharmacist or clinician which symptom relief is appropriate for you, especially for a child or during pregnancy.

Call emergency services immediately for trouble breathing, swelling of the face or throat, widespread hives, collapse, severe weakness or confusion after vaccination. These can signal a serious allergic reaction and need urgent assessment.

Contact the vaccination clinic or a doctor if fever is persistent, symptoms are worsening rather than settling, the injection site becomes increasingly painful or swollen, or you develop another reaction that concerns you. Mention the vaccine name and when it was given.

Useful questions include whether this is a live attenuated or inactivated vaccine, which ingredients it contains, how your medical conditions or medicines affect suitability, when another dose is due, and what reactions should prompt a call. If travel or an animal exposure is relevant, explain the destination, timing or exposure clearly because the recommended vaccine and schedule may change.