Are refugees arriving in Denmark an under-immunised group for measles? A cross-sectional serology study

BACKGROUND: In 2018, Europe faced the highest number of Measles cases in a decade. In Denmark, the childhood vaccination programme has a coverage of approximately 90%. To eliminate the disease, vaccine coverage needs to be above the herd immunity threshold of 95%. This can be even more difficult to obtain, when vaccination programmes break down due to war, natural disasters etc. and concern has been raised, that unvaccinated refugees could facilitate spread of measles when migrating.

METHODS: In order to address this concern, we tested 513 newly arrived refugees and family reunified refugees aged between 0 and 70 years for measles IgG antibodies. The participants were tested as part of a general health assessment between May 2016 and October 2018. In the cohort, 50% were males and the majority came from Syria (55%).

RESULTS: We found that 85% of the total group of refugees had immunity against measles. The 15% lacking antibodies were evenly distributed between the various countries of origin. Moreover, we found immunity to increase with age, leaving young children most vulnerable to infection, 79.9% (<19 years) vs 89.1% (≥19 years). Interview questions on previous vaccinations did not correlate to serology.

CONCLUSION: Refugees have measles immunity slightly lower than the host population.