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close this bookImmunization Policy, 1996 (WHO - OMS, 1996, 63 p.)
View the document(introduction...)
View the document1. Introduction
View the document2. Vaccines used in the EPI
View the document3. Basic immunization schedules and strategies
View the document4. The expected effect of immunization on disease epidemiology
View the document5. Additional schedules and strategies
View the document6. HIV infection and immunization
View the document7. Reactions following immunization
View the document8. Other vaccines that can be used as a part of EPI
View the document9. References

7. Reactions following immunization

Although modern vaccines are extremely safe, some vaccines may lead to reactions. The occurrence of an adverse event after the administration of a vaccine, however, does not prove that the vaccine caused the symptoms. An association between an adverse event and a specific vaccine is suggested:

· if there is an unusual clustering of a condition in vaccinees in a limited interval after immunization, or

· if vaccinees experience the event at a rate significantly higher than that in groups of similar age or background who have not recently received a vaccine.

Adverse reactions may be caused by faults of administration (programmatic errors) or be associated with the properties of vaccines.

7.1 Programmatic errors

The most common adverse events caused by programmatic errors are abscesses following inadvertent inoculation into the superficial layer of the skin of poorly mixed adsorbed vaccines (sterile abscesses), and abscesses that arise because needles and syringes are not sterilized properly. Serious adverse events may arise if vaccines are given to persons for whom they are truly contraindicated, for example BCG and measles vaccines can cause disseminated disease in immunosuppressed individuals.

7.2 Reactions related to inherent properties of vaccines

Adverse events may be caused by reactions to the immunizing antigen itself or to other components of the vaccine, such as antibiotics (kanamycin or neomycin in measles vaccine, streptomycin or neomycin in OPV), a preservative (merthiolate, a mercury-containing compound present in DPT, DT and TT) or aluminium adjuvant present in adsorbed vaccines.

Adverse events range from mild (for example, a transient fever or local irritation following DPT vaccine) to serious (e.g. vaccine-related paralysis following OPV immunization). Mild local reactions following DPT vaccine are quite frequent and occur in 20% - 50% of vaccinees. Rarely occurring sterile abscesses have been reported following immunization with vaccines containing an increased amount of aluminium adjuvants (Bernier 1981). Fever and rash after administration of measles vaccine and tenderness, redness and swelling after typhoid or cholera immunization are other examples of mild adverse reactions following immunization.

Localized and regional adenitis and prolonged ulceration resulting from BCG immunization may be related to the strain of BCG bacilli in the vaccine and often occur after a change in the source of vaccine used in a country. Some substrains of BCG appear to be more likely to cause adenitis than other substrains. Axillary or cervical lymphadenitis usually heals spontaneously and it is best not to treat the lesion if it remains unadherent to the skin. An adherent or fistulated lymph gland, however, may be drained and an anti-TB drug may be instilled locally. Some authors recommend systemic treatment of severe persistent lesions with erythromycin (Bhandari et al. 1980), while others have tried systemic treatment with isoniazid (Hanley et al. 1985). However, lesions have persisted despite one month of therapy with either drug, and placebo-controlled trials of treatment are needed (Hanley et al. 1985). BCG infection that may occur in immunosuppressed individuals should be treated with anti-tuberculous drugs (Romanus et al. 1993).

Some persons, especially in older age groups, may have a hyperimmune reaction to diphtheria toxoid, or more rarely tetanus toxoid, after receiving booster doses of those vaccines when they have high litres of the respective antitoxin. Some live virus vaccines prepared on hen’s egg tissues, such as yellow fever or influenza vaccines, may have a potential risk for egg-sensitive individuals. However, only a few reactions are clearly associated with specific hypersensitivity.

Severe reactions are extremely rare. Major reactions include encephalitis after mumps and measles vaccines, encephalopathy after pertussis vaccines, and paralysis after oral polio vaccine among recipients of the vaccine or their contacts. The risk of OPV-related paralysis has been estimated through passive surveillance in the USA, where about one case has occurred per 2.5 million doses of OPV distributed during 1980-1989 (Strebel et al. 1992). Many adverse events have been reported as related in time to DPT immunization. However, a comprehensive analysis of the relationship between various events and immunization against pertussis did not indicate a causal relationship between DPT immunization and infantile spasms, Reye’s syndrome, or sudden infant death syndrome. There is insufficient evidence to indicate the presence (or absence) of a causal relation between pertussis immunization and aseptic meningitis, chronic neurological damage, Guillain-Barre syndrome, haemolytic anemia and other conditions (Howson and Fineberg 1992a). On very rare occasions, DPT immunization may cause acute encephalopathy, convulsions, or shock-like state or hypotonic and hyporesponsive episodes (Cody et al. 1981, Howson and Fineberg 1992b).

Although the rates of serious events are difficult to estimate precisely, they are far less frequent than the complications caused by the disease themselves (Table 11).

Table 11. Estimated rates of adverse events following DPT and measles immunizations per 100 000 injections compared to complication rates of natural pertussis and measles per 100 000 cases.- According to Galazka et al. (1984)

Condition

Pertussis

Measles


Pertussis disease

DPT immunization

Measles disease

Measles immunization

Encephalopathy/encephalitis

90-4000

0.2

50-400

0.1

Convulsions

600-8000

0.3-90

500-1000

0.02-190

Death

100-4000

0.2

10-10000

0.02-0.3

The detection of serious adverse events following immunization is important for the success of a programme, since such events can influence community acceptance of immunization. In developing countries, the majority of complications recognized following immunization appear to be programme related; thus the underlying causes of these cases need to be identified and corrected.

The policy recommended by EPI is:

· All immunization programmes should monitor adverse events following immunization. A field guide for surveillance of adverse events has been produced (EPI 1993f). Each adverse event should be investigated and efforts should be made to determine its cause. The detection of adverse events should be followed by appropriate treatment and communication with parents, health workers, and if several persons are affected, with the community. If the adverse event was determined to be due to programme errors, operational problems must be solved, by appropriate logistical support, training and supervision.