Monitoring the process of measles elimination by serosurveillance data: The Apulian 2012 study

In 2003 Italy adopted the National Plan for Measles and Congenital Rubella Elimination, but some outbreaks of measles are still occurring, as the target coverage rate (≥95%) for new-borns has currently not been achieved. In order to support the monitoring of the measles elimination programme, the authors carried out a survey about the seroprevalence of measles among Apulia young adults. The study was carried out from May 2011 to June 2012 among blood donors of the Department of Transfusion Medicine of Policlinico General Hospital in Bari. Subjects were enrolled by a convenience sampling. For each enrolled patient we collected a 5mL serum sample. Collected sera were tested by chemiluminescence (CLIA) for anti-Measles IgG. We enrolled 1764 subjects; 1362 (77.2%) were male with a mean age of 38.4±11.7 years. Anti-Measles IgG titre was >16.5UA/mL in 95.1% (95% CI=94.1-96.1) of enrolled subjects with a Geometric Mean Titre (GMT) of 2.3±0.4, which did not differ dividing the enrolled subjects into age groups. As our data showed, the universal routine vaccination changed the epidemiological pattern among adults, in particular young adults (18-24 years), who showed lowest seropositivity rates; in these groups of population there is a risk of the onset of outbreaks due to the presence of susceptible population. This is a paradox linked to the vaccination strategy: when coverage rates keep sub-optimal, measles is more likely to affect young adults and a higher percentage of complications is expected. According to our data, health authorities have to plan a mop-up strategy to actively offer measles vaccination to susceptible young adults.