A systematic review of clinical studies involving more than two million patients aged 50 years and older suggests a recently released shingles vaccine was far more successful in preventing the painful condition compared to the older vaccine—but also carried greater risk of side effects.

The research, led by Dr. Andrea Tricco, a scientist with St. Michael’s Hospital’s Li Ka Shing Knowledge Institute and associate professor at the University of Toronto’s Dalla Lana School of Public Health, was published by the BMJ.

The adjuvant, recombinant subunit vaccine—sold under the brand name Shingrix—was found to be 85% more effective in reducing cases of shingles, also known as herpes zoster, compared to Zostavax, which is a live-attenuated shingles vaccine available for use in Canada since 2006.

The use of Shingrix did lead to 30% more injection-site adverse events, such as redness or swelling. No statistically significant differences were identified between the two vaccines for serious adverse events and deaths.

“There haven’t been any head-to-head studies comparing the two shingles vaccines, so the results from our systematic review can be employed by policymakers, clinicians, and patients to make their decisions on the use of these vaccines,” said Dr. Andrea Tricco.

“If you have to choose between two vaccines and you have evidence showing that one of the vaccines is a little more effective, or a little safer than the other, then you might be more willing to take the safer and more effective one.”

Shingles is a viral infection that occurs through reactivation of latent varicella zoster virus, which causes chickenpox.

About one in four people will develop shingles in their lifetime and about two-thirds get it after the age of 50.