Varicella seroprevalence in individuals with a negative or unknown varicella history - results from a large travel clinic in Switzerland between 2008 and 2015.

QUESTION UNDER STUDY In Switzerland, vaccination against varicella is not recommended in the basic immunisation schedule. However, for individuals aged 11-40 years who do not have a reliable varicella history the Swiss Federal Office of Public Health recommends either (i) a vaccination or (ii) a serology test and vaccination of those with a negative result. In the Travel Clinic of the University of Zurich, the second strategy is followed. In this study we retrospectively assessed the overall percentage of individuals with varicella-specific antibodies despite a negative history and we examined the influence of age, number of siblings, order of siblings, age difference to siblings and nationality on varicella seropositivity. METHODS Between December 2008 and August 2015, the sera of 1757 individuals with a negative varicella history were tested for varicella antibodies. RESULTS A total of 1593 individuals (91%) had a positive result. We found an increasing trend for varicella seropositivity with increasing age. Those aged less than 40 years were significantly more often seronegative (9.5%) than those aged 40 years and above (6.0%, p = 0.049). Seropositivity was associated with nationality. The percentage of seropositives increased with the number of siblings. CONCLUSIONS Our results indicate that, despite the significant varicella seropositivity differences between those aged below and above, the age of 40 may not be an ideal threshold for performing a varicella serology in individuals with a negative or unknown varicella history. In the age groups above 40, testing for varicella antibodies may be especially reasonable in individuals with no or a small number of siblings and in those of specific nationalities.