ba‐Cenoz 2013.

Study characteristics
Methods	Case‐control study ‐ Spain
Participants	Case (N = 54): children aged 15 months to 10 years with a diagnosis of varicella confirmed by PCR Control (N = 432): matched (1:8) by paediatric practice, district of residence, and date of birth
Interventions	Varicella vaccine
Outcomes	Laboratory‐confirmed cases
Funding Source	Government
Notes	The results of this study show that the varicella vaccine is effective in preventing confirmed cases of varicella, although the effect of this vaccine depends on the number of doses and the time since the last dose. Vaccine effectiveness was 87% for 1 dose and 97% for 2 doses.
Risk of bias
Bias	Authors' judgement	Support for judgement
CCS ‐ case selection	Low risk	Adequate ‐ laboratory‐confirmed
CCS ‐ control selection	Low risk	Adequate ‐ community
CCS ‐ comparability	Low risk	Adequate ‐ matched (1:8) by paediatric practice, district of residence, and date of birth
CCS ‐ exposures	Low risk	Adequate ‐ Navarre vaccination registry ‐ secure record
Summary Risk of Bias assessment	Low risk	Plausible bias is unlikely to have seriously altered the results.