ba‐Hungerford 2014.

Study characteristics
Methods	Case‐control study ‐ Liverpool, UK
Participants	Case was defined as a person (median age 16 years old, upper quartile age 76 years old) living in Merseyside with microbiological confirmation of measles (oral fluid/blood test IgM positive or PCR positive) between 1 January and 14 March 2012 with no history of vaccination within 6 weeks of diagnosis. Cases were identified with a computerised case management database, used by Cheshire & Merseyside Health Protection Team. As the assessment focused on possible transmission settings, cases were excluded from the study if they had travelled outside of the UK in the 2 months preceding the onset of illness. In total, there were n = 71 confirmed cases of measles in Merseyside; 1 case was excluded from the study due to travel outside of the UK, leaving n = 70 cases for random allocation in the study. Controls were defined as asymptomatic persons (no history of fever and rash) with no history of travel outside of the UK in the 2 months preceding the onset of illness in the matched case. The controls were selected at random, matched by general medical practice and age (within 1 year). To ensure that all cases were matched to an appropriate number of controls, 5 potential controls were identified for each case to allow for those who refused to participate or were untraceable; if information could not be obtained for the selected control, another control was chosen according to the same principles.
Interventions	Telephone interviews were undertaken following acquisition of valid consent using an agreed script and a structured questionnaire. Information was collected on demographics and vaccination history. Data were also obtained on community and healthcare settings attended in the 2 weeks preceding the onset of illness in the matched case, therefore any case participants that were hospital inpatients prior to onset were not admitted to hospital due to the measles virus. Information was collected on demographics, vaccination history, community settings visited, and attendance at healthcare settings. The interviews were conducted with a parent or guardian if the case/control was under 16 years of age.
Outcomes	Vaccination status was defined as: (1) vaccinated appropriately for age; (2) incompletely/partially vaccinated for age (> 13 months); (3) under age for vaccination (< 14 months).
Funding Source	Government
Notes	Is not completely clear if vaccination status, collected by interview, was confirmed by the Health Authority. Authors' conclusion: "This matched case‐control study provides further strong evidence that eligible children and young adults who are unimmunized/partially immunized and those who are too young to be vaccinated are at significantly increased risk of measles infection when measles virus is circulating." "This study found that being too young for vaccination increased the risk of measles infection"
Risk of bias
Bias	Authors' judgement	Support for judgement
CCS ‐ case selection	Low risk	Adequate ‐ secure record ‐ laboratory‐confirmed
CCS ‐ control selection	Low risk	Adequate ‐ community control
CCS ‐ comparability	Low risk	Adequate ‐ matched for general medical practice and age
CCS ‐ exposures	Unclear risk	Adequate ‐ is not completely clear if vaccination status, collected by interview, was confirmed by the Health Authority.
Summary Risk of Bias assessment	Low risk	Plausible bias is unlikely to have seriously altered the results.