We have presented data on IgG seroprevalences against measles, rubella, and varicella in a large cohort of migrants entering a refugee camp in Northern Germany during the current crisis. The largest proportion of refugees in this cohort were young adults, and the vast majority of refugees (78%) were males. As such, the described cohort is a representative demographic sample of the general population entering Western Europe during the current exodus that mainly consists of young, male adults [8,9,10]. Also, with regard to regions and countries of origin, our cohort reflects current demographics of the general refugee population currently “on the move”. For example, 78.5% of subjects in our analysis came from the Mediterranean region and 9.6% originated from Africa. This is in accordance with current statistics of the UNHCR, which show that the vast majority of all refugees presently seeking asylum in Western countries come from these regions [11].
Overall, we describe satisfactory seropositivity rates in the analyzed population, in which we observed protection rates of 89.9% against measles, 91.2% against varicella, and 86.6% against rubella. However, these rates are clearly lower than the WHO-demanded threshold of 95% for effective herd immunity against measles and rubella [12]. This finding is consistent with the slightly lower seropositivity rates reported by Toikkanen et al. of refugees entering in 2014/2015 [13] and higher MRV seropositivity rates in refugees entering Germany in August 2016, previously reported by our group [10]. This difference is most likely due demographic and geographical changes in the arriving refugee population.
We also show that vaccination rates are different depending on the refugees’ regions of origin. For example, we observed particularly low seropostivity for varicella in Sudanese compared to Syrian refugees. Overall, 15.4% of tested African refugees in our cohort were seronegative for varicella IgG, compared to only 6.5% from the Eastern Mediterranean and 4.9% from the European region. This is accordance with previously reported poor varicella immunization rates in African refugees, and fits with the seroprevalences of Toikkanen et al. and a recent report of a varicella outbreak amongst Sudanese migrants in a French refugee camp in 2015 [13, 14].
Vaccination is most efficient and important at a young age [15, 16], and, especially, the vaccination of young girls against measles, rubella, and varicella may not only protect the girl and women herself from life-threatening infection courses but, importantly, also prevent intrauterine virus transmission with potentially disastrous outcome for the fetus and baby [17, 18]. Of note, the rate of female subjects unprotected against rubella in our cohort was higher in all age groups compared to their male counterparts—around 20% in all women at fertile age had no anti-rubella IgG.
In many cases, health care at admission to refugee housing is the only access young migrants have to vaccination programs, and, even if they are not granted long-term asylum in their desired country of destination, updated and stringent immunization will—in the long run—help them to live healthy and resistant lives.
Mipatrini et al. recently highlighted several challenges with regard to the implementation of effective refugee vaccination in Europe [19]. The authors mention that stringent vaccination of migrants poses a particular problem because most vaccines require repetitive immunization at regular intervals, but refugees are oftentimes constantly “on the move” and may refuse registration with medical authorities for fear of legal consequences. Furthermore, they are in many cases underinformed regarding their personal immunization status and pending shots. Also, many of the hosting countries are currently undergo economic struggles that prohibit effective coordination between health care authorities of neighboring countries.
To tackle these issues, information campaigns and significant improvement of communication structures among public health authorities of European countries is necessary. Current recommendations for refugees’ first contact with the national health care system in Germany, for example, advise the performing of a basic but thorough clinical screening. By applying the “same high standard medical care as to the general population”, treatment for acute medical problems as well as a closure of possible vaccination gaps should be pursued. All data at initial visit should be collected in a database that, in the long run, should provide the structure for effective communication between European health care providers concerned with migrant care. After transfer of the migrants into their destination community, outpatient and inpatient care providers should collaborate to update personal vaccination schedules as recommended by the national vaccination committee [15]. The authors fully support these recommendations.
One major limitation of our work is that seroprevalence cannot accurately reflect protection rates, as IgG levels wane after immunization, even though the individual might still be protected. However, the analysis of serological samples is currently the only feasible method of assessing protection in the absence of comprehensive vaccine documentation.
Another limitation of the study is that the number of older refugees is small in this cohort, representing the general refugee population. Furthermore, although young children were not the focus of our study, our cohort is only fully representative for inhabitants of the refugee camp who are older than 12 years—we show that, especially, the young subcohorts in our population display high rates of seronegativity against varicella. These results emphasize how important are stringent vaccination programs for children and young adolescents in migrating families. We have previously observed this problem in a similar cohort [10]. Due to the rather recent breakdown of previously functioning health care systems, such as, for example, in Syria, young refugees may especially have suffered from insufficient vaccination programs [2]. Further factors increasing the refugees’ susceptibility to VPD infection, such as physical and psychological stress, malnourishment, overcrowding and poor hygiene during migration, may potentiate this problem [4, 15, 19]. Because refugee children, adolescents and young adults represent the majority of persons currently pursuing immigration into Western Europe, refugee health care providers need to be particularly aware of their medical needs [2, 7, 11, 15].