Widespread, aggressive VZV vaccination has reduced the total number of varicella cases by approximately 85% and the number of moderate-to-severe cases by 95% to 100% [125
]. Now, like the live childhood varicella vaccine, there is a live zoster vaccine that seems to be safe and effective clinically. The results of a prospective, double-blind, placebo-controlled trial of attenuated VZV vaccine designed to prevent zoster and PHN in men and women over the age of 60 were recently reported [126
]. Otherwise healthy adults age 60 years or older (median 69 years) were vaccinated with placebo or an attenuated Oka/Merck-VZV vaccine containing 18,700 to 60,000 plaque-forming units of virus, considerably greater than the approximately 1350 plaque-forming units in the Oka/Merck-VZV vaccine administered to American children since 1995. More than 38,000 recipients of the “zoster vaccine” were followed closely for 3 years. The incidence of zoster in the placebo group was 11.1 per 1000-person years, approximating the results of an epidemiologic survey performed a decade ago, which revealed zoster exceeding 10 cases per 1000-person years in individuals older than 75 years [19
]. The effect of zoster vaccine was impressive; compared with placebo, vaccination reduced the incidence of shingles by 51%, the incidence of PHN by 66%, and the burden of illness by 61%.
Overall, serious adverse effects and deaths occurred in 1.4% of both vaccine and placebo recipients. In more than 6000 subjects who kept daily diaries of minor adverse effects for 42 days, 48% of vaccine recipients reported injection site erythema, pain or tenderness, swelling, and pruritis, compared with 16% of placebo recipients. In the same 6000 subjects, serious adverse effects were significantly more frequent (P = 0.03) in vaccine recipients (1.9%) compared with placebo recipients (1.3%), although no specific serious effects emerged. The relative impact of these side effects on the elderly (age ≥70) compared with younger patients was not examined but might be important in future analyses, because the at-risk population over age 70 years is projected to increase substantially in the coming decades. Although the Oka/Merck VZV vaccine on rare occasions unmasks a childhood immunodeficiency disorder, no cases of disseminated zoster that might have been attributed to zoster vaccine in a person with undiagnosed lymphoma, leukemia, or the like were reported.
In 2006, zoster vaccine received FDA approval for healthy VZV-seropositive adults over age 60. Zoster vaccine increases cell-mediated immunity to VZV in such individuals, and the boost is likely to last for decades. Because zoster and its attendant neurologic complication of PHN are common and serious, it seems prudent to recommend zoster vaccine. The Census Bureau projects that by the year 2050, there will be more than 21 million Americans 85 years of age or older (http://www.census.gov/ipc/www/usinterimproj/natprojtab02a.pdf
Despite the development of a vaccine to prevent zoster, even if every healthy adult in the United States over age 60 years is vaccinated, there would still be approximately 500,000 zoster cases annually, about 200,000 of whom will experience PHN, and stroke, blindness, and myelopathy caused by VZV reactivation. Furthermore, because zoster vaccine is not approved for immunocompromised individuals, neurologic disease produced by VZV reactivation in this population is a continuing problem.