Evaluation of the vaccination programs in France

Epidemiologic monitoring

Objectives of the epidemiologic monitoring
Within the framework of the infectious diseases, the purpose of the epidemiologic monitoring is:
– To measure the incidence and the mortality of a disease and to describe the dynamics of its diffusion in time and space. It also makes it possible to know the characteristics of the subjects reached, in terms for example of age, sex, presence of predisposing factors, profession. This descriptive epidemiology, which extended, initially, of the epidemic phenomena to the whole of the field of the infectious diseases apart from specific blazes, then more recently with the field of the chronic diseases, constitutes the precondition to any thorough epidemiologic analysis.
– To have information uninterrupted allowing to detect an epidemic. The epidemiologic data make it possible to confirm the diagnosis of epidemic, to appreciate of it the width and the extension as well as the medical impact.
– To increase knowledge on the factors of risk of the diseases. A correct description of the methods of occurred of the disease makes it possible to generate assumptions on the factors of risk of the disease which can be explored by the techniques of analytical epidemiology (investigation case-witnesses or of troop). The conclusions of these studies are useful for the choice of the most effective actions of prevention and most efficient. At the time of epidemic phenomena, these same techniques are used to identify the origin of the epidemic in order to as soon as possible set up measurements of control at the level of the source of contamination or the subjects likely to be reached.
– To measure the impact of measurements of prevention and control and to adapt their details of implementation.

Methods of the epidemiologic monitoring
A long time comparable with the obligatory declaration which constituted the principal pillar of it, the epidemiologic monitoring saw its methods diversifying, for better taking into account the specific characteristics of each disease to be supervised (primarily frequency and gravity) as well as the methods of their diagnosis and their assumption of responsibility (primarily clinical or biological diagnosis, disease seen downtown or at the hospital). Thus, in France, the epidemiologic monitoring currently rests on several sources of information, the same disease being able to be supervised by several systems, which facilitates the performance evaluation of each system.
– The obligatory declaration (C). It relates to the diseases justiciable to measurements of control at the international, national or local level. Currently 26 diseases are included in the list of the diseases having to be declared to the doctor-inspectors of public health (MISP) of the departmental Directions of the medical and social businesses (DDASS). Since 1996, InVS was seen entrusting by the Directorate-General of health the operational management of the device of monitoring of the diseases to C at the national level.
– Networks of doctor-sentinels. It is primarily about the Sentinelles network, which is pressed on approximately 500 general practitioners communicating each week through a telematic network the number of cases relating to seven infectious diseases, that they diagnosed in their customers. 

– Networks of laboratories of microbiology. They are networks of laboratories of virology or bacteriology, public and private, which provide in a voluntary and regular way information on the identified micro-organisms or the positive serologies carried out at the time of their activity. They can be general practitioners, being interested in several viruses or bacteria, or specialized, being interested in a precise pathogenic agent. Set up for oldest by the cell epidemiology of the national Laboratory of health, they are currently managed by InVS. 

– National centers of reference (CNR). They are generally research laboratories. With the number of forty of which about half within the Pasteur Institute, they are generally specialized for a precise pathogenic agent. Their mission is multiple: contribution to the epidemiologic monitoring, starting from clinical information accompanying the taking away, alerts by the identification of grouped cases related to a single agent, appraises by the fine study of the stocks and the activities of typing. 

– The obligatory declarations of the causes of death, analyzed by the CépiDC service of Inserm (in the past Inserm SC 8), constitute another interesting source of data of monitoring. 

Specificities for the avoidable diseases by vaccination
The various functions of epidemiology can be illustrated within the framework of the vaccinable diseases. It is however the descriptive epidemiology which is essential in the process of management of the programs of vaccination. The data of epidemiologic monitoring are essential, at the moment of the marketing of new vaccines, to decide relevance and the most adapted methods of their integration in the vaccine calendar. At the stage of follow-up of the programs of vaccination implemented, the data of epidemiologic monitoring make it possible to be ensured of the effectiveness of vaccination and to adapt, if necessary, the calendar of vaccination according to the results observed. As an example, the recommendation to integrate vaccination Hépatite B in the calendar of routine of the child in all the countries, including those where the rate of bearing of the HBs antigen is weak, was based on the incapacity of the strategies of vaccination targeted on groups at the risk to reduce significantly, in the industrialized countries, the incidence of the infection by the virus of hepatitis Of the same B the antirubéoleuse vaccination of the teenagers had an impact limited on the incidence of the rubéoleuses infections during the pregnancy, which led the whole of the industrialized countries to choose, in the second time, for one __._ 

Various methods of follow-up of the avoidable diseases by vaccination
They appear, for the diseases corresponding to the vaccines included in the vaccine calendar, in table 3. All the diseases for which exists an obligation or a recommendation of generalized vaccination are the subject of an epidemiologic monitoring making it possible to evaluate the impact of the implementation of the policy.
C interests only 5 of the vaccine diseases with prevention: tuberculosis, diphteria, tetanus, the poliomyelitis and acute hepatitis B (of which the obligatory declaration is effective as from February 2003).
Measles, the mumps, the grippaux syndromes (as well as chicken pox, not included in the vaccine calendar) are supervised by a network of general practitioners Sentinelles (Unit 444 of the INSERM). The influenza is also supervised by the network of the experts taking part in the regional groupings of observation of influenza (GROG).
The rubéoleuses infections during the pregnancy are followed by a network of laboratories of virology (RENARUB). For each identified case, additional information is collected from the clinician. Until 1996, the neurological complications of measles were also supervised by a network of laboratories (RENAROUG). Since January 2000, within the framework of the elimination of the poliomyelitis, the monitoring of the circulation of the entérovirus by networks of laboratories of virology was reinforced and was set up the RSE (inspection network of the entérovirus)
The hospitalized whooping-coughs are followed by a network paediatric sentinel hospital associating clinicians and bacteriologists (RENACOQ).
The invasive with Hib, méningocoques infections and pneumococci are followed by a network of hospital laboratories of microbiology (EPIBAC).
Some of these diseases also profit from a CNR (see list in appendix 3 and table 3).

Table 1: Methods of monitoring of the "diseases of the vaccine calendar" 

The tools used for the monitoring of a disease subjected to a program of vaccination must adapt to the modifications of the epidemiology of the disease induced by vaccination. We will illustrate this matter through the example of measles. 

Measles belonged to the diseases with C until 1986. On this date, it was decided to withdraw it list, within sight of the very weak performances of this monitoring (approximately 1000 cases per annum were notified at the beginning of the Eighties, for a real annual incidence evaluated with more than 500000 cases). This decision intervened in the context of the installation of the Sentinelles network. This method of monitoring, which appeared indeed adapted to the follow-up of a disease which still remained very frequent, made it possible to measure the impact of rougeoleuse vaccination. From the point of view of the elimination of measles at the European level, new methods of monitoring will have to be implemented. It will be indeed necessary to identify, describe and of investiguer all the residual cases or hearths in order to include/understand the reasons of the persistence of viral circulation and to set up effective measurements of control, in terms of adaptation of the vaccine calendar or modification of the strategies of promotion of vaccination. In this context where the disease would have become rare, a network sentinels would not be rather any more sensitive and would not allow to detect the whole of these cases. Thus in the long term, a return to the obligatory declaration of measles appears necessary. Another aspect of the monitoring will have also to be modified.It is about the definition of a case of as a basis measles being used for the notification. Currently, within the framework of the monitoring sentinel, it is based on only clinical criteria (fever of more than 3 days associated with a generalized eruption and with, either a cough, or a coryza or a conjunctivitis). However, in the context of a rare disease, this definition is not adapted any more, from its lack of specificity, involving a significant proportion of wrongfully positive diagnoses. An English study carried out whereas the annual incidence of the disease was still of approximately 10000 cases, showed that only 36 % of the diagnosed cases as measles by the general practitioners were confirmed at the laboratory. This proportion was only 17 % for the sporadic cases and 11 % for the cases occurring in children of less than 1 year. Since 1994, a biological confirmation of the suspect cases of measles was founded in England. This confirmation rests on the use of a test of detection of IgM in the saliva whose performances were shown comparable with those of the diagnosis serologic. This test was tested in France within the framework of a pilot study and a reflexion is currently in hand on the methods of installation in the future of a biological confirmation of the suspect cases in France. With the approach of elimination, following the example what is already in work for the polioviruses, a genetic analysis of the rougeoleux viruses identified in France will be useful for better knowing the residual transmission chains and making the distinction between imported cases and autochtones. To this end, a national Center of reference for measles was named in 2002.

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