Background: VARIVAX (Oka/Merck) is a live varicella vaccine, licensed in Europe since 2003. In addition to routine safety surveillance, the Varicella Zoster Virus Identification Program (VZVIP) analyzes clinical samples to establish whether adverse events (AEs) are associated with wild-type (wt) or vaccine varicella zoster virus (vVZV) strain. The European VZVIP provides data on VZV clade distribution.
Methods: Samples were collected from patients with selected AEs; the VZV strain was determined using polymerase chain reaction.
Results: From October 2003 to September 2008, 1006 spontaneous AE reports were analyzed (88% non-serious). Samples from 76/585 cases with selected AEs were collected. Of 55 VZV-positive/typable samples, wtVZV was detected in 40 and vVZV in 15 samples. Most rashes (32/44) <or=42 days postvaccination were associated with wtVZV. For breakthrough varicella, 6/9 cases were wtVZV-positive; none were vVZV-positive. For herpes zoster 9/17 cases were VZV-positive: eight vVZV, one wtVZV. One case of mild encephalitis was associated with vVZV. One of three cases of suspected secondary vVZV transmission was confirmed. Most wtVZV was clade 3 and clade 1.
Conclusions: European experience confirms that Oka/Merck vaccine is generally well tolerated. wtVZV genotypes were consistent with the molecular epidemiology of VZV in Europe.