Vaccines, like any other medicine, can cause adverse reactions. These reactions will almost always be mild, rarely moderate, and exceptionally severe.
Technological development and the quality of clinical trials allow the development of effective and safe vaccines. However, and again, as with any other drug, only post-marketing monitoring will allow us to know the real rate of adverse reactions (such monitoring is known as pharmacovigilance). Before vaccines reach pharmacies, they have passed numerous strict clinical trials and have proven their safety and efficacy in hundreds of thousands of children.
Adverse reactions after vaccination can be classified as follows:
1. Reactions induced by vaccination:
1a) Local reactions.
- Common: occur in 5-15% of children after vaccination. They are characterized by pain, swelling, and redness at the puncture site. They are the most frequent, occurring during the first 48 hours after vaccination, and can vary in intensity individually. They subside spontaneously in 1-2 days. It can occur in up to 50% of children after the administration of the DTP vaccine (diphtheria, tetanus and pertussis).
- Rare: 1-10 cases per million doses administered. Those described are: abscess at the puncture site, local inflammatory reaction lasting more than 3 days or local hypersensitivity reactions. None of these rare local reactions leave permanent sequelae, except for possible keloid-type scars (bulging).
1b) Systemic reactions.
- Common: appear in less than 10% of vaccinated children: fever, temporary irritability, muscle pain, malaise, headache, vomiting, or diarrhea. All of them resolve spontaneously and without sequelae. The appearance of spots on the skin or urticaria is more frequent after MMR (measles, rubella and mumps) or chickenpox, equally mild and spontaneously resolved. Arthralgias may occur rarely, especially from the rubella component of MMR, which resolve several weeks after vaccination.
- Rare. Less than one case per million doses administered. Among them, anaphylaxis stands out, a type of serious allergic reaction that can compromise the life of the child, and that can appear after taking any medicine or food. It is not possible to anticipate this type of immediate reaction after vaccination, but it does have treatment and is effective. For this reason, vaccines are administered in health centers, and it is recommended that children remain in the center for a few minutes after being vaccinated. Other exceptional complications would be episodes of hypotonia-hyporesponsiveness and inconsolable persistent crying, in both cases also spontaneous resolution and without sequelae. There are some rare but serious neurological adverse reactions, which have been temporarily associated with the administration of vaccines, although a causal link has not been established. These include: acute flaccid paralysis (related to the polio vaccine), Guillain Barré syndrome, facial paralysis, aseptic meningitis, brachial neuritis, encephalopathies and seizures.
2. Reactions due to program errors:
They are reactions due to any error in the conservation, storage, transport, handling or administration of the vaccines. For example: non-sterile injections, reconstitution errors, injections in the wrong places, improper transport or storage, or ignoring contraindications.
3. Coincident reactions:
They occur when the cause of the adverse reaction coincides with the act of vaccination. That is, it could have occurred even if the patient had not been vaccinated. The best evidence to conclude that an adverse event is coincidental is that it has been diagnosed in people who have not been vaccinated.
4. Idiosyncratic reactions or of unknown cause:
These are reactions that appear in a patient after vaccination, the cause of which does not correspond to any of those mentioned above and, therefore, the cause that produces them is unknown.
Vaccines all present a favorable risk / benefit ratio. A possible reading by parents is that if, for example, in Spain there has been a case of diphtheria in the last 30 years, anaphylaxis seems an unacceptable risk, since one case in a million seems greater than one case in 30 years. This approach, which is very logical, would be valid if 100% of the population were vaccinated and we had closed borders.
The goal is yes, universal vaccination, but borders make less sense every day, and obviously they cannot be closed. We live in a globalized world, and at any time, in any place, whoever sits next to us on the bus, in the restaurant or in the cinema, may not be vaccinated, either by choice or because they have not been lucky. to be able to receive vaccines, and to be a transmitter of immunopreventable diseases.
The decision to vaccinate is free. The risk that we want to assume is also risky. Not vaccinating our children for fear of possible side effects is a valid approach, but we must know the risks of not vaccinating and assume them, not put our hands in the head when certain diseases occur. The misnamed 'anti-vaccine' philosophy is a first world problem. In developing countries, no one can understand that parents do not want to vaccinate their children.
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