Five years have passed since the Food and Drug Administration approved a vaccine against shingles. By now, experts had expected a substantial proportion of people older than 60, the most vulnerable population, to be protected from outbreaks of this nasty viral disease and the persistent, debilitating pain it can leave behind.
Indeed, the vaccine, called Zostavax, could so sharply reduce the number of adults who suffer from shingles — currently more than one million a year — that in March, the Food and Drug Administration approved its use by those ages 50 and older. But even with this weapon at the ready, the campaign against shingles has bogged down. Some experts say it never really got under way.
A combination of factors has dissuaded many physicians' offices and clinics from carrying Zostavax. And its manufacturer, Merck, has been unable to produce sufficient quantities to meet even modest demand.
Intermittent shortages that last months have kept the company from consistently marketing the vaccine and have forestalled public health campaigns that could have built awareness of the need for it.
"It really, really has been frustrating," said Dr. Rafael Harpaz, an epidemiologist at the federal Centers for Disease Control and Prevention. "There hasn't been a single year since the vaccine was licensed in 2006 that there's been no problem with supply."
As a result of these obstacles, just 10 percent of adults 60 and older were vaccinated against shingles in 2009, the most recent federal survey reports — far fewer than scientists and public health officials originally had hoped. (By comparison, two-thirds of those 65 and older got a flu shot that year.)
And with Zostavax again in short supply, a C.D.C. advisory committee in June declined to vote on whether to recommend the vaccine for people in their 50s, even though the F.D.A. had already approved it for that group.
"Maybe it's not appropriate to expand a vaccine when it's not available to the people who can most benefit from it," Dr. Harpaz said. "How much more disease might you cause by diverting vaccine to a younger group at lower risk?"
This stalemate was not what researchers had in mind when they began gearing up to test the vaccine in 1992. If ever there was an opportunity to advance public health, they knew, this was surely it. Virtually the entire adult population harbors the virus that causes shingles, called varicella zoster, and each one faces a one-in-three chance of developing shingles at some point.
The virus causes childhood chickenpox, then goes dormant for decades. When reactivated in later adulthood — how that happens is not well understood, though the risk rises with age — the virus causes a hallmark rash. The lesions typically last 7 to 10 days and heal in two to four weeks, but the scarring and pigment changes can be permanent.
About half of shingles victims describe the pain as "horrible" or "excruciating," the C.D.C. has reported. In 10 percent to 25 percent of cases, the virus attacks an eye and can permanently impair vision.
The severity of symptoms increases with age: 18 percent of all patients experience postherpetic neuralgia, nerve pain which can linger for months or even years after the rash clears, according to one decade-long Minnesota study.
Among those over age 79, the incidence of shingles climbs to 33 percent. Prompt treatment with antiviral drugs can reduce the severity of the outbreaks but hasn't been shown to prevent the neuralgia, which can disrupt sleep and work and, if it continues, lead to depression and social isolation.
"You can have your life ruined," said Dr. Michael Oxman, an infectious disease researcher who led the first large clinical trial demonstrating the vaccine's effectiveness.
Researchers and federal regulators long ago agreed, therefore, that their priority is to protect older adults. In 2005, to much fanfare, Dr. Oxman and his colleagues at 22 research sites reported that the vaccine produced a 51 percent reduction in outbreaks of shingles and a 67 percent reduction in postherpetic neuralgia in patients age 60 and older.
The researchers also found that the vaccine was less likely to prevent disease in those over age 80. Yet a subsequent community study of more than 300,000 adults age 60 and older at Kaiser Permanente health centers in California — more closely reflecting real-world conditions — found that the vaccine reduced shingles by 55 percent across all age groups.
"The burden of the disease is so great that reducing it by half is a real public health benefit," said Dr. Harpaz of the C.D.C.
The vaccine also lowered the rate of ophthalmic cases and of hospitalizations, indicating that even when it doesn't prevent shingles, "the vaccine can alleviate symptoms," said Hung-fu Tseng, a research scientist at Kaiser Permanente and lead author of the study.
But although Merck managed to ship two million doses in the first half of this year, more than in any previous full year, Zostavax is once more in scant supply.
The vaccine is made with a live attenuated virus that has proved difficult to grow in bulk, and also is needed to make the childhood chickenpox vaccine, said Dr. Eddy Bresnitz, global medical affairs director of Merck Vaccines.
The company is spending $1 billion to increase production and has built a new manufacturing plant in Durham, N.C. But it won't be fully licensed and operational until 2013, Dr. Bresnitz said.
Even when it's available, Zostavax is the most expensive adult vaccine, selling for about $160 a dose, not counting the cost of an office visit and injection. Few insurers will currently cover the cost for patients under age 60.
Because the vaccine must be stored frozen and few doctors' offices are equipped with freezers, many patients must turn to pharmacies for the shot. Fortunately, pharmacies can bill Medicaredirectly, under Part D, whereas physicians are reimbursed under Part B and therefore may require patients to pay for the vaccine themselves, then file for reimbursement.
That outlay alone discourages many older adults from getting vaccinated, research has shown. Patients in their 50s also must shoulder the cost, since many insurers are reluctant to covervaccinations the C.D.C. hasn't officially recommended. Every year, shingles strikes 200,000 adults ages 50 to 59.
"If someone 52 came to me worried about shingles, I'd vaccinate him," Dr. Oxman said. "The only toxicity I'm aware of is to the wallet."
Patients may also require an eventual booster, since it is not yet clear how long the vaccine remains effective.
But that's a less urgent matter than getting people at risk vaccinated in the first place.
Directly or indirectly, "the public foots the bill for all this research," Dr. Oxman added. "So I'm disappointed that a much higher proportion of those who would benefit from the vaccine haven't gotten it. We ought to be able to do a lot better than this."