Why do complications occur after vaccinations?

All vaccinations have the properties of reactogenicity, that is, the ability to cause local and general symptoms, but to date, complications after vaccinations are rare. Between reactions and complications it is difficult to draw a line, the latter include serious disorders. An acute episode can either have a cause-and-effect relationship with the vaccine, or be a coincidence; it should be considered an "adverse event" before the end of the investigation. The presence or absence of a causal relationship can be proven or probable - in the absence of conclusive evidence for or against.

It is important to evaluate the event after vaccination in terms of its compliance with pathology, which can be observed during a natural infection. Examples are paralysis in VAP and in case of infection caused by wild virus, serous meningitis after mumps vaccination, typical for this infection, arthropathy after rubella vaccination, reminiscent of that after rubella. But intestinal disorders that are not characteristic of whooping cough, diphtheria or tetanus is difficult to connect with DTP.

In instructions to vaccines, benign, reversible in a short time and fairly frequent reactions (fever, rash, redness and soreness at the injection site, rash, etc.) are indicated as well as more rare events (shock, thrombocytopenia, etc.). ), which should be considered a complication.

Monitoring the safety of vaccines requires that all serious health disorders be taken into account after the introduction of the vaccine in order to respond in a timely manner if they become more frequent. So in the US, reports of several cases of intestinal invagination after the introduction of the Rotashild vaccine, created on the basis of monkey rotaviruses, have allowed the timely discontinuation of its use.

Causes of complications after vaccinations

1. Non-compliance with contraindications - usually a lack of account of allergy (to chicken protein, aminoglycosides, rarely to yeast) or signs of primary immunodeficiency (paraproctitis, lymphadenitis, phlegmon). 
2. Programmed (procedural) complications are violations of the vaccination technique: sterility (suppuration at the injection site), subcutaneous administration of adsorbed vaccines (infiltrates), subcutaneous injection of BCG (infiltrate, lymphadenitis). The risk of BCG entering the muscle or under the skin with instrument contamination predetermined a ban on the introduction of BCG and other vaccines in the same room. When vaccinated in dressing, there were cases of dilution of vaccines with muscle relaxants, insulin. Re-use of disposable syringes is a threat of HIV infection and hepatitis B and C. 
3. Systemic errors of vaccination.
4. Complications due to individual sensitivity are the most frequent cause of reactions: allergic (rash, urticaria, shock), neurologic (convulsions, encephalopathy). They are described in Chapters 2 and 3, their treatment is given below. 
5. Indirect events related to vaccination. This, for example, simple febrile convulsions against the background of the temperature caused by DTP, injecting nerve injury with the introduction of the vaccine into the buttock. Sometimes (for example, with the development of the first episode of afebrile convulsions after DTP), this event has to be recognized as a complication, although usually subsequent follow-up and EEG show that the vaccine was only a trigger for an epileptic attack. 
6. Intercurrent disease in the post-vaccination period; To prove the non-involvement of the vaccine, 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 non-severe reactions, can not be attributed to complications.

[1], [2], [3], [4], [5], [6]

Systemic vaccination errors

Inadequate quality of the vaccine

A substandard vaccine is a drug:

• issued in violation of the requirements of regulatory documentation;
• changed the properties due to violation of transportation and storage conditions;
• stored in the opened multi-dose packaging for non-compliance with requirements.

Over the past 40 years, complications associated with a poorly produced vaccine in the USSR and Russia were not. Another thing is the inadequate safety of the vaccine as such, with the same type of complications, 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 monitor whether complications are associated with a single vaccine series, because it can speak of defects in its production; a series of vaccines in these cases is subject to verification.

Inadequate quality of the preparation is indicated by mechanical impurities or non-breaking flakes in sorbed preparations, turbid liquid preparations, changes in the form of the lyophilized preparation or the time of its resuspension. The labeling, the integrity of the ampoule (vial) should also be checked. The changed physical properties in several boxes with the drug require the suspension of the entire series.

Infringements of conditions of transportation and storage of a vaccine

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

Dose dysfunction

Dose violation, in addition to the vaccinator's error when administering the vaccine, may arise when the dry preparation is not properly resuspended, mixed in a multidose package, and the subcutaneous administration of vaccines prepared for cutaneous administration.

[7], [8], [9]

Application by mistake of another vaccine

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

[10], [11], [12], [13], [14], [15]