Genotyping of different varicella vaccine strains

BackgroundLittle is known about single nucleotide polymorphism (SNP) in different lots of varicella vaccines distributed by the manufacturers. Recently, the genetic analysis of several genomic regions revealed a polymorphism in different vaccine lots of Varilrix® manufactured by GlaxoSmithKline. These findings need attention since mutations in the vaccine strain could result in changes of virulence and efficacy of the vaccine.ObjectivesTo identify SNPs in three varicella vaccine lots of Varilrix® and to compare the results with that of Varivax® as well as the published sequences of the Oka vaccine strain (V-Oka) and its parental virus (P-Oka).Study designThe open reading frames (ORF) 1, 6, 10, 21, 50, 54, and 62 were analyzed by sequencing of amplified DNA fragments.ResultsWild-type nucleotides identical to that of P-Oka and/or the European wild-type reference strain Dumas and in contrast to V-Oka could be identified in ORF 1 of a Varilrix® vaccine lot distributed in 1991. In the ORF 62 probably responsible for attenuation of V-Oka, this vaccine strain contained 16 SNPs which were nearly all wild-type-like. By contrast, different lots of the Varivax® vaccine revealed uniform sequencing results. The vaccine Varilrix® 1999 showed a high similarity to the Varivax® vaccine currently available.ConclusionsThe obvious genetic diversity of different lots of the varicella vaccine Varilrix® cannot be explained with the coexistence of several strain variants in the vaccine, but most likely with different seed lot preparations used for vaccine production.