Information for health-care workers - managing adverse events
WHO recommendations on minimizing AEFIs
Most of the AEFIs reported can be linked to improper handling of measles, BCG or yellow fever vaccine when the administration of vaccine had been contaminated during handling and stored until a subsequent immunization session, or to the reconstitution of vaccines with an inappropriate diluent.
In some health centres and hospitals many potentially dangerous medications are kept in the same refrigerator in which vaccines are stored. These medications are packed in similar vials or ampoules to vaccines or their diluents and may be used by mistake for reconstitution of vaccines. In the examples given on the previous page, this probably happened in two countries where muscle relaxant drugs (pavulon or anectine) were incriminated. The onset of symptoms was rapid in these cases, occurring within minutes with cyanosis, hypotonia, dyspnoea or apparent shock symptoms. The affected children had "hypersalivation", most probably due to inability of swallowing saliva because of pharyngeal and throat muscle paralysis. In one country, investigation of urine revealed a metabolite of succinyl choline.
Unsterile procedures during reconstitution of vaccines and/or storing and using reconstituted vaccine over a number of immunization sessions results in administration of contaminated vaccine. BCG and yellow fever vaccines have no preservative at all and measles vaccine can contain only traces of antibiotics. Therefore, rapid multiplication of the infecting pathogen can take place, especially when reconstituted vaccine is kept outside of the refrigerator.
Contamination of reconstituted measles vaccine with Staphylococcus aureus has been documented in several case histories in different countries. Children immunized with contaminated vaccines become sick within a few hours; local tenderness and tissue infiltration, vomiting, diarrhoea, cyanosis and high temperature are the most frequent symptoms. Events are usually associated with immunization from one vial, while many other doses of the same lot are administered in the same or other countries with no reactions. These incidents, which result in needless deaths or life threatening illness, and damage to immunization programmes, are completely preventable if proper reconstitution of vaccines and proper handling procedures are followed. WHO recommends that:
- measles, BCG and yellow fever vaccines should be reconstituted only with the diluent supplied by the manufacturer;
- reconstituted vaccines should be discarded no longer than six hours after reconstitution or at the end of each immunization session, whichever is earlier, and NEVER retained for use in subsequent immunization sessions;
- in the refrigerator of the immunization centre, no other drugs and substances should be stored beside vaccines. Labels should be carefully read before a vaccine is prepared for administration; if the label cannot be clearly read and there is doubt about the contents of a vial or ampoule it should not be used;
- immunization workers should be trained and closely supervised to ensure that proper procedures are being followed. This is essential to the prevention of deaths or injury following immunization; and
- careful epidemiological investigation should be carried out in the event of an adverse event following immunization. The complete investigation of AEFIs is of critical importance to pinpoint the cause of the incident and to correct wrong immunization practices.
Further information on WHO's policy on the use of opened multi-dose vials of vaccine and the procedures for proper handling and reconstitution of vaccines to avoid programme errors can be found in: