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The aim of this study was to evaluate the level of poliomyelitis immunization in refugees residing in the Asylum Seeker Center in Bari. The study was carried out during 2008 and involved 573 refugees. An antibody titer ≥1:8 was found in 99.6% for poliovirus 1, in 99.8% for poliovirus 2, and in 99.5% for poliovirus 3.
In 1988, the World Health Assembly resolved to eradicate poliomyelitis worldwide by the year 2000.1 Thanks to the consistent implementation of vaccination strategies, the number of endemic countries decreased from 1252 in 1988 to 4 (Nigeria, India, Pakistan, and Afghanistan) in 2008 with a >99% reduction of paralytic polio cases. During 2008, in countries where poliomyelitis was still endemic, 1,506 new cases were registered, while in countries where poliovirus is not endemic, 146 sporadic cases were notified.1
The WHO European Region has been free of autochthonous polio cases from 1998, and certification by the WHO in 2002 of this condition led to a modification in vaccine administration. The oral polio vaccine (OPV) has gradually been replaced with the enhanced potency inactivated polio vaccine (IPV), safer than OPV because it is not associated with the rare risk of vaccine-associated paralytic poliomyelitis (VAPP).3
In Italy, there is an increased and continuous inflow of refugees from countries where poliomyelitis is still present and this may represent a risk of the wild poliovirus strains being introduced. The Italian region of Puglia (Southern Italy) can be deemed a “border region” because, due to its geographic position, it has to face daily arrivals of refugees.
The aim of this study was to evaluate the poliomyelitis immunization level, by titration of the neutralizing antibody, in a sample of refugees of various nationalities residing in the Asylum Seeker Center in Bari Palese in Puglia.
The study was carried out during 2008 and involved 573 refugees, 520 (90.8%; 95% CI = 88–92.9) males and 53 (9.2%; 95% CI = 7.1 − 12) females. Of these, 546 (95.3%; 95% CI = 93.1 − 96.8) were from Africa and 27 (4.7%; 95% CI = 3.2 − 6.9) from Asia. In particular, 20 residents (3.5%; 95% CI = 2.2 − 5.4) were from Afghanistan and 67 (11.7%; 95% CI = 9.2 − 14.7) from Nigeria. The average age of the population sample was 24.3 (SD = 5.4; range 1–50).
Signed informed consent to the study was obtained from each participant. A 10 mL blood sample was obtained by venipuncture and the serum was separated by centrifugation. Each serum sample was coded and stored at −20°C. The immunity against poliomyelitis was evaluated as described previously.4
Demographic data from the Asylum Center database and the laboratory exam results were analyzed with the statistical software Epi-Info 6.00. Fisher's exact test was used in the analysis of the difference between proportions. A value of p < 0.05 was considered as significant.
An antibody titer ≥1:8 was found in 571 subjects (99.6%) for poliovirus type 1, in 572 subjects (99.8%) for poliovirus type 2, and in 570 subjects (99.5%) for poliovirus type 3 (Table 1).
Table 1. Antibody titers against poliovirus type 1, 2, and 3, by home continent of refugees
|Poliovirus type 1|
|Asia||0||0.0||0||0.0||0||0.0||2||7.4||25||92.6|| || |
|Total||2||0.3||0||0.0||13||2.3||40||7.0||518||90.4|| || |
|Poliovirus type 2|
|Asia||0||0.0||0||0.0||0||0.0||1||3.7||26||96.3|| || |
|Total*||1||0.2||0||0.0||5||0.9||22||3.8||544||95.1|| || |
|Poliovirus type 3|
|Asia||0||0.0||0||0.0||0||0.0||0||0.0||27||100|| || |
|Total||2||0.3||1||0.2||6||1.0||31||5.4||533||93.1|| || |
All the subjects with an antibody titer less than 1:8 were males from Africa: specifically, a 20-year-old Nigerian with antibody titer less than 1:4 for the three types of poliovirus; two Somalis, aged 26 and 20, had antibody titers of 1:4 and 1:8, respectively. The levels of antibody titer did not significantly differ between Africans and Asians (Table 1).
Our survey results revealed excellent immunization levels in the immigrants, in line with other studies in Europe in the last 15 years.5,6 However, we cannot exclude the existence of low-immunity pockets in the immigrant population just because they were not detected in our study. In fact, in Italy, there are about 3,000,000 immigrants with residence permits, but there are estimated to be about 500,000 illegal immigrants,7 which is a problem for our country because it is difficult to ascertain their origin and their health condition, since they often refuse contact with the health authorities because of fear of expulsion.
Immunity levels to polio and reasons for immunity have changed over the last ∼20 years in many developing countries in Africa and Asia. Many of the older adults in our survey will have immunity to one or more polio types due to natural infection. However, with the elimination of polio in many countries, immunity in children and young adults is often due only to vaccination. In several African countries the vaccination coverage against poliomyelitis has not reached optimum levels, although governments and humanitarian organizations have made numerous efforts in organizational and monetary terms.8,9 Wars and especially religious beliefs, have presented obstacles to a thorough diffusion of polio vaccination. In the light of this, periodic assessment of immunity levels in the population and particularly in the more vulnerable sub-populations, like immigrants and refugees, is necessary. This must be done together with environmental monitoring of viral circulation and surveillance of acute flaccid paralysis. Such a protocol could guard against the reintroduction of poliovirus in countries certified polio-free, as has recently occurred in some countries where the level of immunization in the general population was low.10
It is also necessary to guarantee that all immigrant and refugee children receive or have already received vaccination against poliomyelitis, as provided by the Italian laws for minimum levels of assistance for its population. This will prevent the forming of pockets of susceptible people. The CDC currently recommends that unless foreign born persons can provide a vaccination record documenting receipt of recommended immunizations or other evidence of immunity, they should receive age appropriate vaccines.11 Our study found that the great majority of primary refugees lacked documentation for the recommended immunizations. It is also advisable that the Medical Offices of the Asylum Seeker Centers give immunization certificates for the vaccines administered to the immigrants during their residence.
Environmental surveillance in Puglia shows a residual circulation of Sabin 1-like poliovirus, presumably recently introduced by immigrants from countries which use OPV. This possible spread of vaccinal viruses is a worrying development, as they have an annual mutation rate of 1 to 2% among the new cohorts of infants vaccinated with IPV, and so might lead to the selection of neurovirulent strains.12