Vaccination against varicella as post-exposure prophylaxis in adults: A quantitative assessment
Introduction
Varicella is a ubiquitous, highly contagious childhood disease due to the varicella zoster virus. In western countries, nine teenagers out of 10 have evidence of past infection in the absence of vaccination [1], [2]. In those who are infected in adulthood, the disease is usually more severe with complications including death [3], [4], [5], [6], [7]. Adults account for 26% of hospitalizations and 69% of deaths related to varicella, although they are only 10% of the cases [3].
To reduce the burden of disease when universal vaccination is not recommended, targeted primary vaccination of non-immune adolescents and adults as well as post-exposure vaccination may be considered [8], [9], [10]. However, recommendation for vaccination in adolescents have been poorly followed by general practitioners and the public, mostly due to ignorance or opposition [11].
Post-exposure vaccination, in the 3 days following exposure, prevents up to 90% infections and reduces severity [12], [13], [14]. A quantified assessment of the benefit of this recommendation may help inform professionals and patients and allow effectiveness analysis. We therefore set out to estimate the number of cases of varicella that could be avoided if a recommendation of post-exposure varicella vaccination was applied.
Section snippets
Methods
To estimate the impact of post-exposure prophylaxis in adults, we modeled the risk of varicella during the lifetime of a non-immune adult aged 18. In case of identified exposure to varicella, adults with a negative or unknown history of varicella would be proposed vaccination, irrespective of their real immunity as no time would be spent for serotesting. We assumed that identification of varicella exposure would be possible only in case of infection in close relatives, for example in the
Results
Between 2011 and 2013, 221 cases of varicella were reported to the Sentinelles network in adults aged more than 18. Among those, 81 (37%) reported a familial contact prior to infection. Using this data in our Bayesian framework led to estimate that an average number of μE = 6 (95% CI [2; 13]) varicella exposures during one's lifetime were necessary to reach a lifetime varicella risk of 80% in non-immune adults. The risk of infection after an exposure was 32% (95% CI [16%; 43%]). One varicella
Discussion
When universal varicella vaccination is not recommended, several measures may be adopted to reduce the burden of the disease in adults. Vaccination of all non-immune adults and adolescents would be cost-effective [15] but has proved difficult to apply [11]. More limited vaccination recommendations, like post-exposure prophylaxis, could be more easily accepted, but its impact is unknown. Here, we have shown that post-exposure varicella vaccination of adults in a country without universal
Conclusion
Applying the French recommendations for post-exposure vaccination against varicella in adults with an uncertain history of varicella could prevent 26% of cases and 31% of hospitalizations in adults if vaccination acceptance is 70%. The number to vaccinate to prevent one infection would be 16, and 889 to prevent one hospitalization, making an assessment of efficiency possible. The application of this recommendation in countries without universal vaccination could therefore significantly reduce
Conflicts of interest statement
The authors declare that they have no competing interests.
Authors’ contributions
TH and PYB conceived the study. EB, CS carried out the analyses and drafted the manuscript. CT, TB provided data. All authors contributed to the final manuscript and approved the final version as submitted.
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