On the heels of the Food and Drug Administration approval of Shingrix , a new vaccine from GlaxoSmithKline for the prevention of shingles, a federal committee of immunization experts voted Wednesday to recommend Shingrix for all Americans 50 and older.

Shingles, also known as herpes zoster, is a painful, itchy rash that develops on one side of the body and can last for two to four weeks. One in three Americans will develop shingles in their lifetime, with the risk increasing to half of adults over 85, according to the US Centers for Disease Control and Prevention.

The Advisory Committee on Immunization Practices, which advises the CDC on vaccine usage, also recommended that adults who received Zostavax, a shingles vaccine made by Merck, be revaccinated with Shingrix.

Additionally, the committee expressed its preference for Shingrix over Zostavax.

GlaxoSmithKline says Shingrix will be available "shortly."

Zostavax was licensed and recommended by the committee in 2006 for people 60 and older, including those who have had an episode of shingles. Until now, it has been the only approved vaccine to protect against the virus.

Vaccine differences

Vaccines "teach" the body's immune system how to identify and protect itself against a virus or microbe it has not come into contact with.

Shingles is caused by a reactivation of the varicella zoster virus, the same virus that causes chickenpox.

Zostavax, a live-attenuated vaccine, introduces a weaker (attenuated) version of the varicella zoster virus in order to stimulate the immune system.

By comparison, Shingrix is a non-live, subunit vaccine that works by introducing only an essential subunit of the actual microbe. The intention of using part rather than the whole pathogen is to reduce the possibility of the body having an adverse reaction.

Zostavax is a single-shot vaccine that is given once. Shingrix is also a one-time-only vaccine, yet two shots are given two months apart.

Between 10% and 18% of patients will experience a complication known as postherpetic neuralgia, which causes pain and lasts from three months up to several years, once the shingles rash is gone.

Studies presented to the committee show that Zostavax is 51% effective against shingles and 67% effective against postherpetic neuralgia.

In contrast, Shingrix is 97% effective against shingles for people between the ages of 50 and 69 and 91% effective for people 70 or older. It is 91% effective against postherpetic neuralgia for people 50 and older. These rates are based on evidence presented to the committee from clinical trials with over 38,000 total participants.

Both vaccines wane in effectiveness over time. Zostavax diminishes in effectiveness by 15% to 25% after the first year and shows no significant protection by the ninth year, according to research presented to the committee. Shingrix remained at or above 85% effectiveness up to four years after vaccination; longer-term effectiveness is unknown.

Committee considerations

About 31% of the US population age 60 and older -- about 20 million people -- has been vaccinated with Zostavax, which is considered high uptake for an adult vaccine, according to the CDC.

More than one committee member suggested that familiarity with shingles -- and the serious pain it can cause -- accounts for this unusually high rate of acceptance. There are an estimated 1 million cases of shingles in the nation each year, according to the CDC.

Deliberating before the vote, the committee examined the cost-effectiveness of the two vaccines by estimating the total price of each vaccine and the costs when people become ill and compared the relative economic impacts.

The committee also considered possible challenges to giving adults two shots of a vaccine instead of only one. Real world data on other two-dose vaccines suggest that some people do not get both doses.

With little fuss, the majority of the 15-member committee voted both to recommend Shingrix and revaccination with it.

The pre-vote debate became lively, though, when considering whether to prefer Shingrix over Zostavax for the prevention of shingles and related complications.

"It's not so much a matter of not preferring (Shingrix); it's a matter of not preferring this vaccine at this particular moment in time," said Cynthia Pellegrini, the solo consumer representative on the committee.

Though eight members voted in favor of preferring Shingrix, Pellegrini and six others voted against the motion.

She would rather the committee "wait a year or two and get a little bit more data about the real-world uptake implications of this vaccine," she said.

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Pellegrini admitted that Shringrix has been studied "very extensively" for almost a decade.

Though the clinical studies included a large number of participants, she noted that participation rates among ethnic minorities were "quite low." Different population groups, then, might have bad reactions to the vaccine not yet seen by the scientists, she said.

Though outvoted on the preference issue, she voted in favor of recommending Shingrix for everyone over 50 and revaccination for those who had received Zostavax.