Information for health-care workers - managing adverse events
Expected rates of AEFIs
Estimated AEFI rates following some childhood vaccines
| Vaccine | Estimated rate* |
| BCG | 1 in 1 000 - 1 in 50 000 doses |
| OPV (oral polio vaccine) | 1 in 2-3 million doses (or 1 in 750 000 doses for the first dose) |
| Measles | 1 in 1 million doses |
| DTP | 1 in 750 000 |
* Only the rate for severe reactions has been quoted.
As disease incidence declines due to effective immunization programmes, the occurrence of AEFIs will receive more attention. AEFIs may occur coincidentally after immunization (see above), some events may be caused by faults in the storage, handling and administration of the vaccine (programmatic error), and some may be associated with the properties of vaccines themselves. AEFIs due to programmatic errors in the storage, handling, or administration of vaccine are more common than AEFIs due to the properties of vaccines. Monitoring of AEFIs is important for the success of the immunization programme, since such events can influence community acceptance of immunization. Careful surveillance and investigation of AEFIs are necessary to identify causes of these events that require correction. The most common errors linked with immunization are listed below.
Errors which can lead to AEFIs
- Too much vaccine given in one dose.
- Improper immunization site or route.
- Syringes and needles improperly sterilized.
- Vaccine reconstituted with incorrect diluent.
- Wrong amount of diluent used.
- Drug inadvertently substituted for vaccine or diluent (can result from inattention when reading labels on vials resulting in mistaken content).
- Vaccine prepared incorrectly for use e.g. an adsorbed vaccine not being shaken properly before use.
- Vaccine or diluent contaminated.
- Vaccine stored incorrectly.
- Contraindications ignored e.g. a child who experienced a severe reaction after a previous dose of a vaccine is immunized with the same vaccine.
- Reconstituted vaccine used beyond six hours after reconstitution or not thrown out at the end of an immunization session and used at a subsequent one.