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Objective. Varicella breakthrough, the occurrence of varicella disease >42 days after vaccination, is indicative of vaccination failure. A sevenfold increased risk of breakthrough among vaccinated children with asthma was observed in a 1996 varicella outbreak in a child care center. More recent outbreak investigations have also identified age at vaccination as a potential risk factor for breakthrough. We assessed the association of varicella breakthrough with asthma, steroids, age at varicella vaccination, and timing of measles-mumps-rubella (MMR) vaccination. Methods. We performed a retrospective cohort study among children born after 1993 and followed up through 1999 at 2 health maintenance organizations ([HMOs] A and B) in the United States. Information was obtained from automated vaccination, clinic, hospital discharge, and pharmacy records. Results. We identified 268 and 97 breakthrough cases among 80 584 and 8181 children vaccinated against varicella at HMOs A and B, respectively. Varicella breakthrough was not associated with asthma, inhaled steroids prescribed at any time, and oral steroids prescribed before vaccination. An increased risk of varicella breakthrough was found in the 3 months immediately after prescription for oral steroids at HMO A (adjusted relative risk [aRR]: 2.4; 95% confidence interval [CI]: 1.3-4.4) and HMO B (aRR: 2.8; 95% CI: 1.0-7.8), when varicella vaccine was given before 15 months of age at HMO A (aRR: 1.4; 95% CI: 1.1-1.9), and when varicella vaccination followed MMR vaccine within 28 days at HMO A (aRR: 3.1; 95% CI: 1.5-6.4). Conclusions. Varicella vaccine failure in children... [ABSTRACT FROM AUTHOR]

Background: Varicella is generally considered a mild disease. Disease burden is not well known and country-level estimation is challenging. As varicella disease is not notifiable, notification criteria and rates vary between countries. In general, existing surveillance systems do not capture cases that do not seek medical care, and most are affected by underreporting and underascertainment. We aimed to estimate the overall varicella disease burden in Europe to provide critical information to support decision-making regarding varicella vaccination.Methods: We conducted a systematic literature review to identify all available epidemiological data on varicella IgG antibody seroprevalence, primary care and hospitalisation incidence, and mortality. We then developed methods to estimate age-specific varicella incidence and annual number of cases by different levels of severity (cases in the community, health care seekers in primary care and hospitals, and deaths) for all countries belonging to the European Medicines Agency (EMA) region and Switzerland.Results: In the absence of universal varicella immunization, the burden of varicella would be substantial with a total of 5.5 million (95% CI: 4.7-6.4) varicella cases occurring annually across Europe. Variation exists between countries but overall the majority of cases (3 million; 95% CI: 2.7-3.3) would occur in children <5 years. Annually, 3-3.9 million patients would consult a primary care physician, 18,200-23,500 patients would be hospitalised, and 80 varicella-related deaths would occur (95% CI: 19-822).Conclusions: Varicella disease burden is substantial. Most cases occur in children <5 years old but adults require hospitalisation more often and are at higher risk of death. This information should be considered when planning and evaluating varicella control strategies. A better understanding of the driving factors of country-specific differences in varicella transmission and health care utilization is needed. Improving and standardizing varicella surveillance in Europe, as initiated by the European Centre for Disease Prevention and Control (ECDC), is important to improve data quality to facilitate inter-country comparison. [ABSTRACT FROM AUTHOR]