Effectiveness of varicella vaccine as post exposure prophylaxis in Chilean children Introduction: Efficacy and effectiveness of varicella vaccine (VV) as post exposure prophylaxis (PEP) strategy have shown discordant results for disease risk reduction, and more consistent results in their ability to attenuate the disease. Aim: To assess the effectiveness of VV as PEP among household contacts. Material and Methods: We followed up 33 children after household exposure to a varicella case, of which 15 received VV as PEP and 18 did not received VV. The presence and severity of the disease were clinically determined. Results: Secondary attack rate was 53% among vaccinated and 89% among non-vaccinated children. Overall effectiveness of VV as PEP was 40% (CI95% 1%-64%). The effectiveness for preventing moderate or severe disease was 63% (CI95% 8%-85%) in the entire group and 77% (CI95% 14%-94%) among children vaccinated during the first 3 days post exposure. Vaccine tolerance was acceptable, with a low number of adverse reactions, all of them mild. Conclusion: The results suggest that VV as PEP is effective among household contacts, especially for reducing the severity of the disease.