Discussion

Our study evaluated serological protection against tetanus in immigrant children. As in the studies on adult refugees, [10,11] a large percentage of immigrant children did not have vaccination records on arrival. While only about half of the patients' parents recalled that their children had received at least the tetanus vaccine dose, more than 96% of the children responded to a single vaccination with protective levels and therefore did not require additional update vaccinations. This represents a much higher rate of protection than predicted by the literature, in which only 35- 87% of adopted children or immigrant patients had protective levels of antibodies against tetanus. [4,12] This could be explained by a high percentage of children from Eastern Europe with, until recently, high vaccination coverage and the absence of children from China, which seems to be a particularly vulnerable population. [12] The effect of United Nations World Health Organization / Children's Fund campaigns in sub-Saharan Africa may also have played a role, but due to the heterogeneity of our population it was not possible to analyze each country separately. Furthermore, most of the children arrived in good clinical condition, without malnutrition or HIV infection, which may explain their good past and present immune capacity.

The serotest after a single vaccination identified sufficiently immunized children and avoided many unnecessary additional vaccinations. He identified the few children who most likely had never been vaccinated before or who had not generated enough memory B cells; their post-booster antibody levels remained <1,0 IU / mL. Although this has not been formally tested here, the serum response of a single (possibly "booster") vaccination is likely a better predictor of a previous tetanus vaccination / baseline immunity than baseline antibody measurements; post-immunization responses reflect the persistence and "recall" of specific memory B cells and may persist long after the antibody disappears. [13]

The results of our study should discourage starting complete vaccination programs without serological tests in immigrant children, because most children, even when they claim they have never been vaccinated, did not need a complete recovery. It could also expose them to the risk of hyperimmunization. Although mild adverse reactions to vaccination have not been systematically recorded in the patient records, no serious adverse reactions have been reported, even for our patients with very high antibody responses. This suggests that their basal tetanus titers were low at the time of recall, avoiding the generation of inflammatory immune complexes. Although this cannot be demonstrated, it is likely that the high or very high titres elicited after the first booster would have generated more serious adverse events if additional immunization had been empirically administered.

This study reports our results for tetanus immunity; however, immigrant children often have poor immune coverage for other vaccine-preventable diseases. [14] Recently, Paxton et al. [14] confirmed that almost all pediatric immigrants in their institution from East Africa had an unknown or incomplete vaccination status and only 15% of the children presented with serological immunity against tetanus, hepatitis B, diphtheria, rubella or measles. In addition, several authors also showed that even after resettlement, patients were not properly vaccinated and had missed many opportunities, such as medical visits, for the recovery of vaccinations. [5,14] Still today, immigrant children they remain a vulnerable group for health problems, despite the recommendations available. In our institute we design vaccination programs based on the patient's age, vaccination records (if available) and risk factors (Table 2). We usually administer a maximum of 3 vaccines simultaneously for convenience and inject live attenuated vaccines both simultaneously and 4 weeks apart, as recommended. [9] The recovery program started on the first visit and is completed as quickly as possible afterwards (2-6 months) to protect the children as quickly as possible and before their residence status is decided. All parents receive a copy of the vaccination records and the new primary pediatrician also receives a copy in case the children become resident. Our study was not designed as a cost analysis study. However, the costs of measuring antibody titers, which vary from country to country, were much lower than the costs of additional combined vaccines containing tetanus. In addition, we used an anesthetizing skin cream to significantly reduce the discomfort of phlebotomy, although this method has shown little effectiveness in reducing the discomfort of intradermal vaccination.

Our study has some limitations. First, we did not have enough patients to determine the predictive factors for vaccine responses based on the country of origin (and their vaccination schedules), age or gender. Larger studies would be needed to identify these subgroups and define vaccination strategies based on demographic data. Furthermore, since many of our patients came from Eastern Europe, it is possible that our conclusions do not apply to children from Asia or Latin America. Secondly, there is a small percentage of children who respond suboptimally to vaccination against tetanus as well. Therefore, it is possible that children with low antibody titers were "poor responders" rather than under vaccinated children. However, low responders benefit from additional boosters, making this difference more academic than clinically relevant. Third, antibody titers have not been evaluated before booster vaccination, precluding identification of the percentage of children in whom even the single booster could be avoided Consider our national guidelines to provide recovery immunization as soon as possible to migrant children who may not benefit from prolonged follow-up -up doctor, we should have done a clinical study design. Although this study is theoretically feasible, it was considered problematic in this vulnerable population that was unfamiliar with research studies, had communication problems, had interaction times limited and other factors. Finally, we opted eg r the determination of tetanus antibodies as a single representative element for immunization for DTP and childhood poliomyelitis, which can be oversimplified. It is possible that tetanus antibodies are not a good representative element of pertussis immunity since antibodies to pertussis seem to fade more quickly over time and require an earlier booster dose. [15] However, combined childhood vaccines containing inactivated tetanus, diphtheria and whooping cough and polio viruses are usually given at the time of DTP immunization, polio specific serology is neither readily available nor standardized and the risk of acquiring poliomyelitis is currently low in most countries.

All refugee children should be checked for vaccination status on arrival. We recommend measuring tetanus antibody titers after a single age-appropriate vaccination to evaluate tetanus immunity as a representative element of previous DTP and poliomyelitis vaccinations. This strategy allows individual customization of vaccination programs, avoids many unnecessary vaccinations and decreases the risk of hyperimmunization.