Herpes zoster vaccine is safe and effective for older adults

Question Can a vaccine prevent herpes zoster and postherpetic neuralgia?

Synopsis Patients with herpes zoster (shingles) feel miserable, and postherpetic neuralgia—which complicates about 10% of cases—makes them feel even worse. This study identified people over 60 (47% were over 70) who had either a history of varicella or were presumed to have one because they had lived in the United States for at least 30 years. A total of 59% were men, 95% were white, and they had a generally good baseline health status. Patients were randomised (allocation concealed) to either 0.5 ml of live attenuated Oka/Merck varicella-zoster virus vaccine (n = 19 270) or placebo (n = 19 276). The vaccine is 14 times stronger than the vaccine used to prevent primary varicella infection in children. Groups were balanced at baseline and analysis was by intention to treat. Patients were followed for a median of 3.1 years, and 95% completed the study, which is excellent. The primary outcomes were the number of episodes of herpes zoster and postherpetic neuralgia; cases within 30 days of vaccination and second episodes were excluded. Fewer patients in the vaccination group developed herpes zoster (11.1 v 5.4 episodes per 1000 person years; P < 0.001; number needed to treat = 175 per year). Patients in the vaccinated group also had a somewhat shorter course (21 v 24 days; P = 0.03) and were less likely to develop postherpetic neuralgia (0.48 v 1.38 per 1000 person years; P < 0.001; NNT = 1111). The benefit was more pronounced in patients aged 60-69 than in older patients. Safety is an important issue in prevention studies since we are treating otherwise healthy patients. Safety was monitored in two ways: by patient's or physician's report for the entire population, and by diary entries for a subset of 6716 patients. For the entire study population, there was no difference in mortality between groups and no difference in possible vaccine-related adverse events, either during the first 42 days or for the duration of the three year study. For the group in a substudy of adverse events, one or more adverse events—primarily erythema, pain, swelling, or pruritus at the injection site—occurred more often during the first 42 days. As noted above, this is a higher potency vaccine; the vaccine currently used for children should not be used for adults.

Bottom line Herpes zoster vaccine is safe and effective for the prevention of herpes zoster and postherpetic neuralgia in older adults. The number needed to treat is quite large on an annual basis—even if the NNT of 1111 is linear for a 10 year period, 111 older patients would have to be vaccinated to prevent one case of postherpetic neuralgia during that period. The number needed to treat to prevent a case of herpes zoster is 175. Given the strength of this vaccination and the target population, long term follow-up studies are needed to identify any unexpected but serious complications that may appear down the road.

Level of evidence 1b (see www.infopoems.com/levels.html). Individual randomised controlled trials (with narrow confidence interval).