Elsevier

Vaccine

Volume 33, Issue 3, 9 January 2015, Pages 446-450
Vaccine

Vaccination against varicella as post-exposure prophylaxis in adults: A quantitative assessment

https://doi.org/10.1016/j.vaccine.2014.11.045Get rights and content

Highlights

  • Adults post-exposure varicella vaccination has been recommended but is poorly adopted.

  • Post-exposure vaccination after familial exposure would cut adult cases by 26%.

  • Sixteen adults would be vaccinated to avoid one varicella case.

  • Post-exposure vaccination leads to a substantial decrease in the burden of varicella.

Abstract

Background

Varicella can be severe in adults. When universal vaccination is not adopted, post-exposure prophylaxis has been recommended in adults with uncertain history of varicella to reduce the burden of the disease in adults, however its impact is not quantified.

Methods

We developed a Bayesian probabilistic framework to estimate the impact of post-exposure prophylaxis in adults. We hypothesized that post-exposure vaccination would be proposed only after varicella exposure in close relatives. Information regarding the nature of the culprit exposure was obtained from a sample of 221 adult varicella cases. The lifelong probability that adults aged 18 would be infected with varicella was determined using data from the French Sentinelles surveillance network. Estimates of post-exposure vaccination efficacy were then used to compute the number of cases and hospitalizations prevented in adults.

Results

Familial exposure to varicella was reported by 81 adult cases out of 221. The probability of infection after exposure was 32%, so that six exposures on average were necessary to explain the observed cumulated lifetime incidence of varicella in non-immune 18 years old and over adults. Among the 35% of the 18 years old population with uncertain history of varicella, 11% would truly be non-immune. Post-exposure vaccination would prevent 26% of the cases (13 cases prevented per 100,000 adults per year) and 31% of the hospitalizations (0.2 hospitalizations prevented per 100,000 adults per year) if vaccination acceptance was 70%. An average of 16 adults would be vaccinated to avert one varicella case.

Conclusions

Post-exposure vaccination is associated with a substantial decrease in the burden of the disease in adults in a country where universal vaccination is not recommended. This quantitative information may help inform professionals to uphold the recommendation.

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.

References (30)

  • A. Gershon et al.

    Varicella vaccine

  • Ministère de la Santé et de la protection sociale. Avis du conseil supérieur d’hygiène publique de France, section...
  • P. Bonanni et al.

    Varicella vaccination in Europe – taking the practical approach

    BMC Med

    (2009)
  • A.M. Arbeter et al.

    Varicella vaccine studies in healthy children and adults

    Pediatrics

    (1986)
  • Y. Asano et al.

    Protection against varicella in family contacts by immediate inoculation with live varicella vaccine

    Pediatrics

    (1977)
  • View full text