The aim of this chapter is to provide the clinician with information to better understand the principles of vaccination and of solving various practical problems which may be encountered in a person coming to be vaccinated. The immunization schedule, updated regularly by health authorities, is easily accessible and therefore will not be detailed here.
Immunization mimics infections that naturally generate protective immunity: introducing an antigen induced in a host a specific reaction resulting in the establishment of a share specific effector mechanisms for the protection against infection, and Furthermore an immune memory.
The only induction of an antibody, however, is not synonymous with efficiency when the antigen mobilizing effectors of the immune reaction is not vital to the microorganism. for example can be seen in most chronic infections (AIDS, syphilis, etc.) that continue to evolve despite the emergence of multiple antibodies. For these persistent infections or does not induce protective immunity, the design of a vaccine still represents a challenge, imposing imagine immune defense mechanisms that do not occur naturally in humans.
The choice of route of vaccine administration (oral, subcutaneous, intramuscular or intradermal) is important because it directs the quality of the response. Thus, the mucosal administration induces the production of secretory antibodies (IgA), useful for blocking the infections by mucosally. This response is also accompanied by a production of antibodies capable IgM and IgG serum. The oral polio vaccine is one example.
The intramuscular or subcutaneous vaccine induces especially the appearance of serum antibody IgM and IgG.Finally, the intradermal administration of the vaccine will result in a cellular response delayed type hypersensitivity, as is the case with BCG.
There are different types of vaccines that can be classified according to their bacterial or viral nature, live or inactivated. Live vaccines swarm from the inoculation site and multiply in the body, the immune response taking place in multiple locations. They usually induce cellular and humoral immunity of good quality, durable, close to that naturally acquired. Inactivated vaccines, antimicrobial agents or complete subunits cause an immune response that is either away from the injection site, at the level of the spleen in particular in the case of soluble antigens, either at the site of injection in the case of particulate antigens in the lymph nodes that drain the region where the vaccine was injected.The immunogenicity of inactivated vaccines is lower than that of live vaccines, requiring repeated injections (Box 1).Primed used 2 to 3 injections one month apart is necessary to induce the primary response. Reminders enable a secondary type response ensuring good vaccine protection and extended memory. The addition of an adjuvant, aluminum hydroxide most often enhances the immunogenicity by increasing the influx of inflammatory cells and the secretion of cytokines at the injection site. In addition, the adjuvant delays the elimination of the antigen, which thus remains longer in contact with the antigen presenting cells and lymphocytes responsible for the specific immune response.
Box 1. Spacing doses
When a delay occurred in the implementation of the said schedule of vaccinations, it is not necessary to repeat the entire vaccination program requiring repeated injections. He did enough to take this program to the point where it was interrupted and complete the vaccination by means of the number of injections required based on age.
Conversely, it is considered invalid injection made 5 or more days before the scheduled date.
The vaccine response varies from one individual to another and even the most effective vaccines will not be immunogenic in all. The genetic background may make some individuals ill recognize a vaccine antigen and thus will be poor responders to the vaccine.
Age is also taken into account. For example, children under 2 years will respond poorly to polysaccharide vaccine subunit and adults see the strength of their immune response flex from 40 years. Women of childbearing age, the same age, have a stronger immune response than men. Finally, immunosuppression decrease the ability to properly respond to vaccination (cancer, chronic renal failure, AIDS, alcoholism and many other conditions).
The effectiveness of a vaccine, that is to say its ability to significantly reduce the incidence of infectious disease in vaccinated subjects compared to subjects who did not receive the vaccine can not be measured with epidemiological techniques. We must therefore make the field of randomized clinical trials, during epidemics, to determine the percentage reduction in attack rate (defined as the proportion of the population having been infected at the end of an epidemic) in vaccinated compared to unvaccinated.
By extrapolation from serological results collected during vaccine efficacy studies in the field, the serum antibody titer can predict vaccine efficacy, but it is as an indirect measure of efficiency.
The prevalence of an infectious disease, as well as its severity or its economic weight are essential inputs for assessing the effectiveness of a vaccine. Thus, a vaccine to protect 100% against a rare, little serious or inexpensive, may have less interest in ensuring that vaccine protection of 40% against a widespread disease, severe and costly.
Recall that the vaccine provides protection not only individual (direct), but also gregarious (indirect). Thus, in non-vaccinated, the number of contacts with infectious is mitigated in a partially vaccinated population, reducing the risk of infection.
The immunization schedule is developed taking into account several parameters:
– Age: Some infections are more serious in the very young child (pertussis) or in the elderly (eg influenza);
– Sex: for example rubella is especially severe during pregnancy;
– Economic considerations: it is an argument to consider the generalization of the vaccine against chickenpox;
– The most recent epidemiological data: for example, a measles epidemic of adolescent risk resulting from insufficient coverage today in France requires a catch-up vaccination in children aged three to six years;
– Individual risks increasing the frequency or severity of infection: profession, travel, sexual behavior, or particular disease state.
In France there are vaccine requirements for certain categories of the population: children (diphtheria, tetanus, polio, BCG), the armed (meningococcal A + C, rubella in women), health professionals (tetanus, polio, BCG, hepatitis B, typhoid and for laboratory personnel).
Most vaccines, however, are more legally “required” but “recommended”, thus respecting the freedom of each health.
They are rare. We must examine and consider any person to whom we will administer a vaccine, looking for an indication against-temporary or permanent vaccination (Box 2). These findings must be recorded in the health record.In France, the updated reference vaccine against-indications are those listed in the summary of product characteristics and on the immunization schedule.
Certain situations or conditions against vaccine-show:
– Scalable acute diseases: it is better to postpone the vaccination and wait for healing;
– Progressive malignant diseases: against-indication of live vaccines, except BCG;
– Immune congenital or acquired deficits, including immuno-depressant treatments: against-indication of live vaccines, including BCG if defi cit of cellular immunity;
– Allergic diseases: only anaphylactic reactions to a vaccine in a previous injection-against indicate subsequent injections of the same vaccine;
– Progressive neurological diseases: pertussis vaccination is against-indicated (history unrelated to vaccination convulsions are not a cons-indication to vaccination);
– Pregnancy: live viral vaccines are an against-indication. However, a vaccination made during an unknown pregnancy does not justify advising termination of the pregnancy;
– HIV infection: live viral vaccines are cons-indicated, BCG can be given to asymptomatic even with a good level of immunity. Inactivated vaccines can be administered as directed by the immunization schedule, without the need to do more (it is not recommended, for example, especially these subjects vaccinated against influenza, pneumococcus andHaemophilus infl influenzae b).
Box 2. Six questions before vaccinating
How are you today ?
Do you have any allergies to foods or medications?
Have you well tolerated in previous vaccinations?
Do you have a disease of your immune system?
Are you pregnant, or are you trying to be?
Have you received any blood product for one year (transfusion, immunoglobulins)?
Besides efficiency, the safety requirement is crucial to the development of a vaccine, and to keep the trust of the physicians and the public.
No vaccination may be considered 100% safe, even if all is well in coming. Possible accidents are twofold.
Mild reactions, frequent, and expected:
They are as follows:
– Fever or malaise;
– Painful nodule at the injection site (especially after vaccine adsorbed on aluminum gel);
– Signs of mild infection with the vaccine virus strain (febrile rash after MMR for example).
Serious and unexpected side effects:
Serious allergic reactions, anaphylactic, are theoretically possible with all vaccines.
Rare but very varied events following immunization are reported: central neuropathy and peripheral cutaneous manifestations, inflammatory joint disease, eye disease, systemic diseases and various autoimmune … The majority of these accidents are clearly that fortuitous associations and not causal , with the vaccine. However, they must be considered before deciding rechallenge the vaccine.
Finally, accidents resulting from poor practice of the vaccine are available: administration of a live attenuated vaccine to an immunocompromised person, or subsequent infection in non-compliance with aseptic technique during injection of a vaccine.
The statement from a pharmacovigilance center of all serious and unexpected adverse reactions is the only way to appreciate the way of present importance which may be the vaccine accidents in comparison to the expected benefits.
The combination vaccines are not to be confused with the combination vaccines, which are to be incorporated in the same syringe more valent vaccine (eg diphtheria, tetanus and poliomyelitis). There is talk of combination vaccine when given simultaneously more than one vaccine at different sites. These associations are very useful for example when preparing consultations trip. When it comes to inactivated vaccines, no association is against-indicated, either with another or inactivated vaccine with a live vaccine. The combination of two live vaccines, rare event, is not recommended for reasons of potential impairment of their effectiveness. A period of four weeks and is recommended between administration of two live vaccines.
By analogy with the combination vaccines include here that the prior administration of immunoglobulins with a higher risk of failure of live virus vaccines such as those against chicken pox, rubella, mumps and measles.
It is against-indicated to vaccinate a patient having received immunoglobulin within 6 weeks (if possible 12 weeks) after administration.
The route of administration of the vaccine is mentioned in the summary of product characteristics.
Non-compliance liable to a decrease in effectiveness of the vaccine and / or an increase in local reactions.Schematically, live vaccines are administered subcutaneously or intramuscularly, while it is recommended to administer the adjuvanted inactivated vaccines intramuscularly avoiding subcutaneously for these.
For patients with disorders of hemostasis, see subcutaneously will be favored, and choose an injection site next to a bone relief for efficient compression after vaccination. Compression must last at least two minutes, five if possible.
In subjects with multiple allergies but no known vaccine allergies, there is no indication against-principle to be vaccinated.
Should be checked with the patient which are the substances responsible for allergies, and make sure it is not a substance used to manufacture the vaccine. Indeed, besides the vaccine antigens, substances such as egg protein, gelatin, neomycin, thimerosal, or latex are found in the composition of vaccines. No vaccine does not contain penicillin or its derivatives. The examination should also confirm the clinical reality of allergy that must be proven (generalized urticaria, asthma, swelling of the face and mouth, difficulty breathing, hypotension, shock) to form a cons-indication. In the proven absence of allergy to components of the vaccine, and in the absence of intolerance to any waning of past vaccinations, vaccines will be administered without special restrictions. It is however not recommended to vaccinate during an outbreak of allergic disease (asthma or hives for example).
In general, it is prudent to ask vaccinated to stay put in order to detect an anaphylactic reaction during a period of at least fifteen minutes after injection or longer if there is a possibility of hypersensitivity. It is also recommended that the doctor is properly equipped to deal with anaphylaxis (epinephrine, corticosteroids, antihistamines, syringes, needles, turnstile …).