The incidence of recurrent herpes zoster following a first episode is comparable to the incidence of a first zoster in the general population.
The study cohort were 267,000 Australians 45 years and over from NSW who consented to long term follow up and linkage of their information in health databases.
Over 1,846,572 person-years, 17,413 participants (6.8%) had a first zoster and 675 of them (0.4%) had a recurrence.
The incidence of a first zoster was 9.43 per 1,000 person years and 0.35 per 1,000 person years for a recurrent zoster.
The study found higher recurrence rates in women compared to men, younger adults (45-64 years) than older adults (≥65 years) and in immunosuppressed compared to non-immunosuppressed participants.
“While the risk of the first zoster episode is known to increase with age due to age-related waning immunity, among those with a first episode this higher incidence of recurrence among younger participants (45-54 years) is intriguing,” the study said.
“A possible explanation for this observation is that the first zoster is more likely in younger participants who are immunosuppressed and therefore they are more vulnerable to a recurrence.”
“However, in our study we also observed the age-difference in those without any reported immunosuppressive conditions. An alternative explanation is that individuals who developed zoster at a younger age may be less capable to control VZV infection because of genetic predisposition.”
The incidence of recurrence was slightly lower in the 12 months after a first zoster but then largely consistent over eight years of follow-up.
The study team, from the School of Public Health and Community Medicine at UNSW, said it was expected that a first episode of zoster should protect individuals against a recurrence by boosting cell-mediated immunity.
“However, we only observed a lower incidence of zoster in those with a prior episode in the first year following the first zoster.”
They postulated that people with a first zoster may have some deficiency in cell-mediated or general immunity resulting in a higher vulnerability to a second reactivation of the virus, or that immunity following a first zoster episode is only boosted for a short period afterwards.
“Our results support vaccination of people who have already experienced an episode of zoster and suggest that this may be beneficial even if administered within 12 months after the first episode.”
“However our results also underpin the need to conduct additional studies on the immunogenicity and efficacy of vaccination in those with a history of zoster.”