A recent study in The BMJ compared the effectiveness and safety of a new herpes zoster vaccine with its older alternative.
The Varicella zoster virus (VZV) is the cause of chickenpox and shingles in humans. Chickenpox most commonly affects children and causes the typical itchy blisters that allow the virus to spread. Healing from chickenpox does not provide protection from a second infection by the same virus. When chickenpox resolves, VZV can lie dormant within the body for decades prior to re-activate and cause herpes zoster, also known as shingles.
Herpes zoster appears as a skin condition but can cause acute, subacute, and chronic neurological conditions. Studies estimated that approximately one person in four is at risk for herpes zoster in their lifetime. The risk is even higher in people over the age of 50. How this virus reactivates and causes disease once again is unknown, but vaccines to prevent infection are available.
Preventing herpes zoster: Live attenuated and adjuvant recombinant subunit vaccines
A live attenuated vaccine to prevent herpes zoster in people of the age of 50 or older is available in most high-income countries. A live attenuated vaccine provides immunity to disease by exposing people to a weakened form of the germ causing illness. Weakened microbes can still induce a response by the immune system but can no longer develop an infection. This vaccine prevents herpes zoster but it is not as effective in people over the age of 70 and is not recommended for individuals with a compromised immune system.
New herpes zoster vaccine recently developed and approved in Canada
Recently, a new herpes zoster vaccine was developed and approved in Canada as well as in a few other countries. The new vaccine is an adjuvant recombinant subunit vaccine. This type of vaccination uses only certain components of microbes as opposed to their whole organism to trigger a response from the immune system. These vaccines are usually cheaper and easier to produce and have a lower risk of side effects. On the other hand, subunit vaccines are generally not as effective as the live attenuated ones.
The availability of two herpes zoster vaccines opens up the debate of which one might be better. A group of researchers performed a comprehensive comparison of the two vaccines to answer this question. Their results were recently published in The BMJ.
The adjuvant recombinant subunit vaccine was more effective than the live attenuated vaccine
The scientists utilized data already available from the literature to compare the two vaccines. A thorough screening of the scientific literature led to identifying the suitable data, which included 27 studies, 22 of which were clinical trials. This data served to perform a statistical analysis to compare the effectiveness and safety of the live attenuated vaccine with the new subunit vaccine and placebo in people aged 50 or older.
The results of this analysis revealed that the adjuvant recombinant subunit vaccine is superior to both the live attenuated vaccine and placebo in preventing herpes zoster infection. In terms of safety, rates of adverse events at injections sites were higher for the subunit vaccine compared with the live attenuated. One limitation of the study is the insufficient amount of data, which prevented the researchers from carrying out some of the pre-planned analyses for a more complete comparison of the two vaccines.
In conclusion, this study compared the effectiveness and safety of a live attenuated and an adjuvant recombinant subunit vaccine for preventing herpes zoster. The scientists used data already available from the scientific literature for their analysis and concluded that the subunit vaccine is more effective at preventing infection. However, this vaccine is associated with a higher rate of adverse events at injection sites.
Several questions remain unanswered
While this analysis is the first comprehensive comparison of the two herpes zoster vaccines, several questions remain unanswered. For example, whether the subunit vaccine is more effective at preventing herpes zoster in people with compromised immune systems is still unknown. Other clinical trials comparing the two vaccines are currently underway and will provide more data in the future to allow for a new, updated assessment.
Written by Raffaele Camasta, PhD
References
- Karch, C. P., & Burkhard, P. (2016). Vaccine technologies: From whole organisms to rationally designed protein assemblies. Biochemical Pharmacology. 120, 1-14.
- Kennedy, P. G. E., & Gershon, A. A. (2018). Clinical Features of Varicella-Zoster Virus Infection. Viruses. 10, (11).
- Tricco, A. C., Zarin, W., Cardoso, R., Veroniki, A. A., Khan, P. A., Nincic, V., Ghassemi, M., Warren, R., Sharpe, J. P., Page, A. V, & Straus, S. E. (2018). Efficacy, effectiveness, and safety of herpes zoster vaccines in adults aged 50 and older: Systematic review and network meta-analysis. BMJ. 363.
