Merck has announced positive results from a Phase 3 trial of V212, an investigational varicella zoster virus vaccine (VZV) for the prevention of herpes zoster (HZ) in immunocompromised patients.

There were 1,230 individuals enrolled (≥18 years old) in the trial, all undergoing hematopoietic stem cell transplants (auto-HSCT). Subjects were randomized to receive a 4-dose regimen of V212 from a consistency lot, a high-antigen lot, or placebo. The patients were followed for an average of 2.6 years post vaccination with cases of HZ confirmed by polymerase chain reaction and/or adjudicated by a blinded data monitory committee. 

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Results showed that V212 met its primary endpoint of reduction in the incidence of confirmed HZ cases by an estimated 64% (95% CI, 0.48, 0.75) in recipients of auto-HSCT. Moderate-to-severe HZ pain also was reduced by an estimated 69.5%, using the Zoster Brief Pain Inventory (ZBPI) score. Other complications, such as hospitalization, disseminated HZ, visceral HZ, ophthalmic HZ, neurological impairment due to HZ, were down by an estimated 73.5%.

The live zoster vaccine, Zostavax (Merck), is approved for those ≥50 years of age and is contraindicated in patients who are immunocompromised. As all individuals receiving auto-HSCT are immunocompromised, if approved, V212 could help reduce the risk of HZ and related complication in this patient population.

Serious adverse events occurred in 32.9% of patients receiving the consistency lot or high-antigen lot and in 32.7% of patients receiving placebo for up to 28 days after the fourth vaccination dose. The most frequent serious adverse event observed was febrile neutropenia in 5.3% of the vaccine group and 4.9% in the placebo group.

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