Earlier this year, plaintiffs who took a vaccine for shingles, known as Zostavax, began filing lawsuits against drug manufacturer Merck & Co., claiming as little as a single dose resulted in serious injuries that include blindness, paralysis, and brain damage. In some cases, the drug was fatal.

The complaint states that Merck failed to issue a proper warning of the side effects as well as defective design and breach of warranty. Now, the Centers for Disease Control and the Advisory Committee on Immunization Practices (ACIP) have weighed in on the issue by giving preference to a new shingles vaccine, Shingrix – a product of Merck rival Glaxo-Smith Kline.

Both Zostavax and Shingrix are classified as “zoster vaccines.” Shingles, or herpes zoster, is a disease that causes painful skin rashes and blisters. Its cause is a virus known as varicella zoster. This particular virus also causes chicken pox. Patients who have had this condition in childhood are generally immune to shingles. Zoster vaccines essentially give a low dose of varicella zoster to the patient in order to activate the immune system against the virus – but ideally, not enough to bring on the disease.

Zostavax was given FDA approval in May 2006. Originally, the vaccine was recommended only for patients 60 and over who did not have a compromised immune system, antibiotic allergies, untreated tuberculosis, or a history of lymphoma or leukemia. Later that year, the CDC recommended that all adults 60 and over be given the vaccine if they had never had chicken pox. In 2011, the FDA approved the use of zoster vaccines for patients as young as 50.

Normally, live zoster vaccine is quite safe; a few patients wind up with a mild form of chicken pox around the injection site for a few days, but beyond that, it is usually harmless. In current lawsuits against Merck, plaintiffs claim that instead of preventing shingles, Zostavax wound up causing the disease. Claimants say they wound up with serious nerve damage and have had to undergo continuing treatments for shingles – the very disease Zostavax was supposed to prevent.

Shingrix was given FDA approval on October 20th, based on the results of the Phase 3 clinical trials demonstrating the vaccine was 97 percent effective in reducing the risk of shingles. At the same time, participants had a lower rate of post-herpetic neuralgia, a painful complication associated with shingles in which patients suffer burning pain long after the visible rashes and blisters have gone. By comparison, Zostavax has been shown to be only 70 percent effective. Furthermore, the protective properties of Shingrix last longer than those associated with Zostavax.

In short, Shingrix is a more effective vaccine – and despite its higher price tag, is more cost-effective in the long run. For this reason, most insurers are willing to pay the difference.

There are a few caveats. A number of ACIP members who voted against the recommendation voiced reservations, citing a lack of long-term safety studies, uncertain supplies, and patient compliance (Shingrix requires two doses whereas Zostavax requires only one). One of the doctors involved in the clinical trials acknowledged that Shingrix “has never been given outside of a research setting…there are a lot of unknowns and there is a lot we need to learn over the next few years.”

Overall, however, the Committee has deemed the advantages of Shingrix to outweigh any risks – enough to recommend it over its competition. Dr. Kelly Moore of the Vanderbilt University Medical Center says, “The evidence before us is this vaccine performs in a very superior fashion and will prevent much more disease than the other product that’s available.”

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K.J. McElrath is a former history and social studies teacher who has long maintained a keen interest in legal and social issues. In addition to writing for The Ring of Fire, he is the author of two published novels: Tamanous Cooley, a darkly comic environmental twist on Dante’s Inferno, and The Missionary’s Wife, a story of the conflict between human nature and fundamentalist religious dogma. When not engaged in journalistic or literary pursuits, K.J. works as an entertainer and film composer.