To the Editor: Cunningham and colleagues discussed the rationale for using a live attenuated vaccine against varicella zoster virus (VZV) in preventing herpes zoster (HZ) in an older population.1 They also noted the difficulties in using a live vaccine in immunocompromised adults.

Although generally considered less immunogenic than its live counterpart, an inactivated VZV vaccine would be ideal for vaccinating immunocompromised hosts. There is little information in the medical literature on inactivated VZV vaccines. However, the studies that do exist tested inactive vaccine on adult populations and showed favourable performance when compared with a live vaccine.2,3 Despite these promising results, the inactivated vaccine seems to have gone out of favour. Furthermore, if an inactivated VZV vaccine was used in the childhood vaccination programs against varicella, then it would simultaneously solve two problems caused by the vaccine strain of the virus, namely the development of infectious varicella and the reactivation of the vaccine strain as HZ.4

Cunningham and colleagues discussed the benefits of vaccinating an older population with VZV vaccine,1 but did not raise the intriguing possibility that the vaccination program might reduce rates of listeriosis in older people.4 A recent study examined the T-cell response in mice to latent herpesvirus infection, and found that it led to activation of macrophages that, surprisingly, protected the host against subsequent infection with other pathogens such as Listeria monocytogenes.5

Given that protection from HZ through vaccination is achieved by stimulating T-cell numbers above a critical threshold for HZ,6 it could be hypothesised that VZV vaccinees may be protected against listeriosis, an infection to which older people are more susceptible. The basis of this hypothesis is that macrophage activity would be stimulated by the T-cell response to the VZV vaccine, thereby providing cross-protection against L. monocytogenes. Prospective follow-up of vaccinees in Australia over time could refute or confirm this hypothesis.