Why do complications arise after immunizations?

All vaccines have reactogenic properties, i.e. the ability to cause local and general symptoms, but complications from vaccinations are rare today. It is difficult to distinguish between reactions and complications, the latter include serious disorders. An acute episode may either have a causal relationship with the vaccine or be a coincidence; it should be considered an "adverse event" until the investigation is completed. The presence or absence of a causal relationship may be proven or probable - in the absence of convincing evidence for or against.

It is important to evaluate the post-vaccination event in terms of its correspondence to the pathology that may be observed during a natural infection. Examples are paralysis in VAP and in infection caused by a wild virus, serous meningitis after mumps vaccination, typical for this infection, arthropathy after rubella vaccination, resembling that after rubella. However, intestinal disorders that are not characteristic of whooping cough, diphtheria or tetanus are difficult to associate with DPT.

The instructions for vaccines indicate both benign, reversible in a short time and fairly common reactions (fever, rash, redness and soreness at the injection site, rash, etc.), as well as rarer events (shock, thrombocytopenia, etc.), which should be considered complications.

Monitoring vaccine safety requires taking into account all serious health problems after the vaccine is administered, so that a timely response can be made if they become more frequent. Thus, in the US, reports of several cases of intestinal intussusception after the administration of the Rotashield vaccine, created on the basis of monkey rotaviruses, allowed its use to be stopped in a timely manner.

Causes of complications after vaccinations

1. Failure to comply with contraindications is usually due to underestimation of allergies (to chicken protein, aminoglycosides, rarely to yeast) or signs of primary immunodeficiency (paraproctitis, lymphadenitis, phlegmon).
2. Program (procedural) complications - violations of vaccination technique: sterility (suppuration at the injection site), subcutaneous administration of adsorbed vaccines (infiltrates), subcutaneous administration of BCG (infiltrate, lymphadenitis). The risk of BCG getting into the muscle or under the skin when contaminating instruments predetermined the ban on the administration of BCG and other vaccines in the same room. During vaccination in dressing rooms, there were cases of dilution of vaccines with muscle relaxants, insulin. Reuse of disposable syringes - a risk of infection with HIV and hepatitis B and C.
3. Systemic errors in vaccination.
4. Complications due to individual sensitivity are the most common cause of reactions: allergic (rashes, urticaria, shock), neurological (convulsions, encephalopathy). They are described in Chapters 2 and 3, their treatment is given below.
5. Indirectly related adverse events. These include, for example, simple febrile seizures due to a fever caused by DPT, or injection trauma to a nerve when the vaccine is administered into the buttock. Sometimes (for example, when the first episode of afebrile seizures develops after DPT), such an event must be recognized as a complication, although subsequent observation and EEG usually show that the vaccination was only a trigger for an epileptic seizure.
6. Intercurrent disease in the post-vaccination period; to prove that the vaccine is not involved, it is important to collect evidence, including laboratory evidence.

Among the causes of adverse events, only the first 4 types are associated with vaccination; types 5 and 6, as well as mild reactions, cannot be classified as complications.

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Systemic errors in vaccination

Poor quality of the vaccine

A poor quality vaccine is a drug:

• issued in violation of regulatory requirements;
• changed properties due to violation of transportation and storage conditions;
• stored in an opened multi-dose package without compliance with the requirements.

Over the past 40 years, there have been no complications associated with poorly manufactured vaccines in the USSR or Russia. Another issue is the insufficient safety of the vaccine as such, in which case similar complications arise, the detection of which leads to its withdrawal. This was the case with the mumps vaccine from the Urabe strain (serous meningitis), with the rotavirus vaccine (see above). It is important to track whether the complications are associated with one batch of the vaccine, since this may indicate defects in its production; in these cases, the vaccine batch is subject to inspection.

Mechanical impurities or flakes that do not break up in sorbed preparations, cloudy liquid preparations, changes in the type of lyophilized preparation or the time of its resuspension indicate poor quality of the preparation. The marking and integrity of the ampoule (vial) are also subject to verification. Changed physical properties in several boxes with the preparation require suspension of the use of the entire series.

Violations of the conditions of transportation and storage of the vaccine

Violation of temperature conditions makes vaccine series inapplicable. Violation of storage conditions of vaccines in opened multi-dose packaging.

Dose violation

In addition to the vaccinator's error when administering the vaccine, a dose violation may occur due to improper resuspension of the dry preparation, poor mixing in a multi-dose package, or subcutaneous administration of vaccines prepared for cutaneous use.

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Mistaken use of the wrong vaccine

The use of another vaccine by mistake is dangerous when using a different route of administration; for example, the administration of BCG subcutaneously or intramuscularly requires specific treatment. The administration of DPT instead of a viral vaccine subcutaneously may be complicated by infiltrate. The administration of OPV parenterally is usually without complications. The fact of an erroneous administration of a vaccine should not be hidden; it is important to consider all its possible consequences and take the necessary measures.

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