Varicella-zoster virus clades circulating in Spain over two decades

Background: Despite childhood universal VZV immunization was introduced in 2015, there are no data on VZV clade distribution in Spain.
Objectives: To characterize the varicella-zoster virus strains circulating in Spain between 1997 and 2016.
Study design: In this retrospective study, we determined the VZV clades in 294 patients with different pathologies (mainly encephalitis, zoster and varicella) by sequencing three fragments within ORF 22, ORF 21 and ORF 50 and, subsequently analyzing 7 relevant SNPs.
Results: Among these 294 patients, 132(44.9%) patients were infected by clade 1, 42(14.3%) patients by clade 3, 19(6.5%) by clade 5, 29(9.9%) by clade VI and 3(1%) by clade 4. Four patients (1.4%) were infected by clade 2 vOKA strains, who received one dose of live-attenuated varicella vaccine. Putative recombinant clade 1/3 was identified in 6 cases (2.0%). Results obtained from partial sequences were assigned to clade 1 or 3 in 56(19%) patients and clade 5 or VI in 3(1.0%) patients. In the multivariate analysis, encephalitis was independently associated with clades 1 and 3 and age >14y.o. (P = 0.035 and P = 0.021, respectively). Additionally, Madrid had significant fewer cases of encephalitis compared with the rest of regions analyzed (P = 0.001).
Conclusions: Higher prevalence of clades 1 and 3 and their relation with encephalitis and age >14y.o. suggest earlier introduction of this clades in Spain. Putative interclade 1 and 3 recombinants are circulating in patients with encephalitis, herpes zoster and varicella. Several cases were related to vOKA vaccination but vaccine strains do not seem to circulate in the general population.