Seroepidemiology of varicella zoster virus infection in Vojvodina, Serbia

Abstract

The present cross-sectional serosurvey constitutes the first effort to describe the varicella zoster virus (VZV) seroepidemiology in Serbia. An age-stratified serum bank of 3570 residual samples collected between 2015 and 2016 in each of the seven districts of the Vojvodina Province was tested for IgG anti-VZV antibodies with an enzyme immunoassay. Results were standardised into common units according to the European Sero-Epidemiology Network (ESEN2) methodology. Univariable and multivariable analyses were used to examine the relationships between standardised anti-VZV positivity or logarithmically transformed antibody titres and demographic features of study subjects. Seropositivity (85% overall) increased with age, in parallel with geometric mean titres. By the time of school entry, 68% of children were immune. The slower subsequent acquisition of immunity leaves epidemiologically relevant proportions of adolescents (7%), young adults (6%) and especially females of reproductive age (6%) prone to more severe forms of varicella. In the ongoing pre-vaccine era, natural infection provides a high level of collective immunity, with the highest VZV transmission in children of preschool age. The detected gaps in VZV immunity of the Serbian population support the adoption of the official recommendations for varicella immunisation of non-immune adolescents and young adults, including non-pregnant women of childbearing age.

Keywords: Antibodies to varicella zoster virus (anti-VZV); ESEN2; Europe; chickenpox; seroprevalence; standardisation; vaccines and immunisation.

Fig. 1.

Sera collection locations at health care institutions in each of the seven districts of the Autonomous Province of Vojvodina, Serbia, 2015–16. The province was divided into three main areas for the purposes of this survey: (a) Northern Vojvodina that included the districts of West Bačka, North Bačka and North Banat; (b) Central Vojvodina that included South Bačka and Central Banat and (c) Southern Vojvodina that included Srem county and South Banat.

Fig. 2.

Anti-VZV ELISA results of the standardisation panel obtained by Serbia (y-axis) plotted against the corresponding results of the reference laboratory (Spain, x-axis) on the logarithmic (base 10) scale. Dotted lines show the equivocal ranges (negative/positive cut-off values), while the solid line represents the quadratic regression model. The only outlier is shown in green.

Fig. 3.

Age-specific standardised seroprevalence of VZV with 95% CIs, in Vojvodina, Serbia, 2015–16.

Fig. 4.

Anti-VZV antibody titres given as geometric mean titres (GMT) expressed in standardised ESEN2 units IU/ml, according to age (a) and according to age and gender (b), in the 3570 study subjects aged 29 days–83 years from Vojvodina, Serbia; 95% CIs are also displayed. The dashed lines indicate the cut-off for positive results (0.05 IU/ml).