Text S1 J48 pruned tree learned on the entire training set starting from the features subset B.  Description of two measles outbreaks in the Lazio Region, Italy (2006-2007). Importance of pockets of low vaccine coverage in sustaining the infection BACKGROUND: Despite the launch of the national plan for measles elimination, in Italy, immunization coverage remains suboptimal and outbreaks continue to occur. Two measles outbreaks, occurred in Lazio region during 2006-2007, were investigated to identify sources of infection, transmission routes, and assess operational implications for elimination of the disease. METHODS: Data were obtained from several sources, the routine infectious diseases surveillance system, field epidemiological investigations, and molecular genotyping of virus by the national reference laboratory. RESULTS: Overall 449 cases were reported, sustained by two different stereotypes overlapping for few months. Serotype D4 was likely imported from Romania by a Roma/Sinti family and subsequently spread to the rest of the population. Serotype B3 was responsible for the second outbreak which started in a secondary school. Pockets of low vaccine coverage individuals (Roma/Sinti communities, high school students) facilitated the reintroduction of serotypes not endemic in Italy and facilitated the measles infection to spread. CONCLUSIONS: Communities with low vaccine coverage represent a more serious public health threat than do sporadic susceptible individuals. The successful elimination of measles will require additional efforts to immunize low vaccine coverage population groups, including hard-to-reach individuals, adolescents, and young adults. An enhanced surveillance systems, which includes viral genotyping to document chains of transmission, is an essential tool for evaluating strategy to control and eliminate measles The World Health Organization Regional Office for Europe (WHO/EURO) has set 2010 as the target for elimination of measles in the region [1, 2] . This objective has already been achieved in some States through routine immunization programmes which maintain high coverage using a two-dose measles-mumps-rubella (MMR) vaccine schedule [3] . However, vaccination coverage still remains inadequate in several western European countries, including Italy, and although mass vaccination has successfully lowered the incidence of the disease outbreaks continue to occur, often affecting communities with low vaccination coverage [4] .