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TLANTA — The expert panel that helps guide U.S. vaccination policy has voted to give a preferential recommendation to GSK’s new shingles vaccine, Shingrix, effectively telling doctors and patients it is better than the alternative on the market, Merck’s Zostavax.

But the preferential vote, a rarity, barely squeaked through, with members of the Advisory Committee on Immunization Practices voting 8-to-7 on the question.

Earlier the committee voted unanimously to recommend the new vaccine, which earned market approval from the Food and Drug Administration last Friday. The vaccine was recommended for use in immune competent adults 50 years of age and older. Data are still being gathered to explore whether the vaccine is safe and effective in immune-compromised individuals, the committee was told.

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ACIP, which advises the Centers for Disease Control and Prevention on vaccine policy, also voted in favor of recommending the vaccine for people who have previously been vaccinated with Zostavax.

Dr. Leonard Friedland, vice president for scientific affairs and public health for GSK’s North American vaccines unit, hailed the decisions as good for patients. He said GSK expects to have the vaccine on the market in the U.S. by the end of November, but it will take until sometime next year before agreements can be worked out with insurance plans to reimburse for the cost of the vaccine.

Shingrix is given in two doses for a total cost of $280 per patient. Zostavax, which only requires one dose, costs $223.

Market analysts have estimated sales of Shingrix could top $1 billion a year in 2022 and further predict it will take a big bite out of Merck’s Zostavax sales.

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Merck’s Dr. Eddy Bresnitz, executive director for adult vaccines, argued against the preferential recommendation before the vote and was disappointed with the outcome.

“We strongly disagree with the vote on the preferential recommendation,” he told STAT. “You could see by the vote it was a split vote, 8-to-7, so virtually a flip of the coin.”

ACIP committee members who voted against the preferential vote raised a number of concerns, including the fact that the GSK vaccine contains a new adjuvant — a compound that boosts the immune impact of the vaccine.

Several voiced reticence to give a preferential recommendation to a vaccine that has only been used so far in clinical trials, while others noted if GSK can’t meet demand for the vaccine, problems could ensue.

Friedland said that shouldn’t be a problem. “We have done careful demand assessments of what we believe the demand will be … and we’re confident that we can meet demand with our production of our vaccine.”

But members who supported the preferential vote said doctors look to the ACIP for advice. Without guidance, they might assume the vaccines were equally effective, argued Dr. Kelly Moore, director of Tennessee’s immunization program.

Dr. Jeffrey Duchin, a non-voting member of the committee who represents the National Association of County and City Health Officials, urged the committee to vote yes.

“How would you explain to a patient why you are not encouraging them to get the better vaccine?” asked Duchin, who heads the infectious diseases and immunization services for Seattle and King County Public Health.

The evidence on the two vaccines that was presented to the committee suggests they are not equal.

Studies have shown Shingrix generates a stronger immune response, even among people in their 70s, who are at high risk of both shingles and the complications of shingles, most notably a painful condition called postherpetic neuralgia.

The vaccine offered 98 percent protection in the first year and that protection remained at 85 percent or higher three years after vaccination. Zostavax offers moderate protection in the first couple of years after vaccination, but that appears to drop off quickly, leaving vaccinated people again vulnerable to shingles and postherpetic neuralgia.

In fact, because the risk of shingles rises with age, Zostavax is not recommended for adults in their 50s. Its recommendation is for adults 60 years of age and older.

The recommendation urging a preferential vote for Shingrix came from a work group of experts advising the ACIP. They suggested a preferential recommendation would avert thousands of cases of shingles and post-herpetic neuralgia.

Shingles is a delayed complication of chickenpox, a highly infectious disease most children contracted in the era before the chickenpox vaccine was developed. Anyone who has had chickenpox is vulnerable to developing shingles.

That’s because the virus that causes chickenpox — the varicella zoster virus — remains dormant in the body after infection. A healthy immune system keeps the virus in check. But people whose immune systems have been weakened by illness, cancer treatment, or the natural decline that comes with age can develop the condition.

There are an estimated 1 million cases of shingles a year in the U.S., and 1 in 3 people can expected to develop the painful condition during their lifetime.

Shingles typically manifests as a painful, itchy rash, either on one side of the torso or one side of the face. The blisters can ulcerate and lead to scars.

While the condition is unpleasant, the complications of shingles can be severe. It can lead to strokes, vision, and hearing loss. It can also lead to postherpetic neuralgia, severe nerve pain that persists for months, and in some cases years. (Ordinary shingles normally clear up within a few weeks.)

The risk of developing postherpetic neuralgia also rises with age. The CDC estimates that for people 60 and older who develop shingles, the risk of postherpetic neuralgia is 1 in 3.

Market projections for Shingrix are strong. EvaluatePharma estimates the U.S. sales alone could reach nearly $600 million a year in 2022. Meanwhile, the forecasting firm projects U.S. sales of Zostavax to tumble from nearly $500 million this year to $337 million in 2022.

EvaluatePharma derives its forecasts by averaging the estimates of a number of stock market analysts; the company does not know whether those source analyses factored in a preferential recommendation for Shingrix.

Zostavax offers moderate protection against shingles and postherpetic neuralgia in the first few years after vaccination — 51 percent and 67 percent, respectively. But the protection wanes quite quickly and appears to be gone within seven to nine years after vaccination.

GSK has followed some people who received Shingrix in its clinical trials for nine years post-vaccination at this point and reports that protection remains high.

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