Luisa Hogan got the vaccine against shingles in 2007, the year after it was approved for people 60 and older.

"My mom had shingles," Hogan, of Malvern, said. "I saw her suffer, so I went and got the vaccine as soon as I learned about it."

But then in April, Hogan developed a blistery purple rash on her lower back, accompanied by searing pain. After her local hospital emergency room diagnosed a kidney infection, she went to her family doctor.

He immediately recognized herpes zoster, better known as shingles.

"I've had children. The pain of shingles is much, much worse," said Hogan, who is also a grandmother. "Like the man on TV says, it feels like a hot poker on my skin."

Hogan, 69, who still has persistent pain, doesn't regret getting Merck & Co's Zostavax. Research suggests her misery might be even worse without the vaccine. But she no longer feels a sense of protection, and she realizes that, common as shingles is, awareness is scanty.

"It's not a sexy disease," she said. "There are no 5K runs for it."

Shingles is related to that childhood bane, chickenpox. After the itchy blisters of chickenpox disappear, the varicella-zoster virus remains in the body, dormant in nerve cells.

Years or decades later, the virus erupts as shingles in one of every four infected adults, more than a million a year. Scientists can't explain this reactivation, but age-related declines in immune protection play a role because shingles usually occurs after age 50, and the incidence steadily climbs with age.

Waning immune function also limits the effectiveness of Zostavax. On average, it cuts the risk of shingles by half in people older than 60, studies show. But the risk reduction shrinks with age: 70 percent in people ages 50 to 59, 64 percent in sexagenarians, and only 39 percent in septuagenarians.

"It's very typical of most vaccines because older people's immune systems aren't as robust," said Eddy Bresnitz, global medical affairs director for Merck Vaccines.

Public health authorities and Merck have been working to raise awareness of shingles and boost vaccination rates. In 2011, fewer than 16 percent of people 60 and older had gotten the shot.

Turning that around hasn't been easy. Until last year, Merck had production problems that restricted supplies. That's why federal vaccine advisers did not recommend Zostavax for ages 50 to 59, even though it is approved for that age group. The vaccine is relatively expensive, about $170, and insurance coverage varies.

In addition, scientists don't fully understand the worst complication of shingles, called postherpetic neuralgia. About 10 percent of people, among them Hogan, suffer from this debilitating nerve pain, which can last for months or years after the rash goes away.

"We think some people are unaware of the disease itself," said Stephanie Bialek, a herpes virus expert at the U.S. Centers for Disease Control and Prevention. "And some physicians and patients are not aware of how severe the disease can be."

A number of therapies have proved effective for the nerve pain, including opioids, capsaicin cream, certain antidepressants, the anti-epileptic drug Neurontin, and Lyrica, a drug used to relieve fibromyalgia and diabetic nerve pain.

"As long as I take my Lyrica, I'm a happy camper," Hogan said. "But I don't want to take it indefinitely."

Chickenpox, of course, is no longer an itchy rite of passage. Since 1995, children have been getting the chickenpox vaccine, Varivax, also made by Merck.

Whether that will free them from shingles in the future remains to be seen.

"The chickenpox vaccine has been around since the '90s," Bresnitz said. "We won't know what impact it will have on herpes zoster for 20 or 30 years."

Contact Marie McCullough at 215-854-2720 or mmccullough@phillynews.com.