The virus responsible for chickenpox, varicella zoster virus (VZV), can remain dormant inside nerve cells. Years later, when a person's immunity declines, for example because of aging, the virus may reactivate and travel through the nerve to the skin surface, producing clusters of blisters distributed along the path of the affected nerve, a condition called herpes zoster or shingles. Itching, numbness, tingling or localised pain precede the appearance of skin lesions. The virus causes inflammation of sensory nerves and can cause severe pain which impacts patients' quality of life. The annual incidence of herpes zoster is currently 5.22 episodes per 1000 older adults. This incidence is increasing, in part due to longer lifespan.
We identified eight randomised controlled trials which enrolled 52,269 participants. The vaccine was effective in reducing herpes zoster by almost 50%. The only adverse effects caused by the vaccine were mostly mild to moderate symptoms at the injection site. The vaccine was more effective in people aged 60 to 69 years, but individuals in this age group were also more susceptible to adverse effects compared to those 70 years or over.
Injection site adverse effects were less frequent in participants receiving refrigerated herpes zoster vaccine than frozen vaccine. The incidence of adverse effects was higher at the second vaccination compared to the first. Participants receiving zoster vaccine had significantly lower rates of one or more injection site adverse effects and pain at injection site than those receiving the 'pneumo 23' vaccine.
The impact of vaccination on quality of life was poorly reported in the included trials. The vaccine reduced the number of participants with severe quality of life impairment caused by acute pain from herpes zoster. Only one of the eight included trials was of high quality, with a low risk of bias. The results currently described in the review may be underestimated. The results of ongoing trials may add relevant data to this interesting and important field of investigation.
The effectiveness of vaccines with lower concentrations of VZV should be tested in order to optimise the viral load used in each dose.