A shingles vaccine advertising campaign promotes shots to prevent an itchy, blistering rash and persistent pain in seniors, but it may not present the full picture.

Shingles occurs when the zoster virus that causes chicken pox resurfaces with age.

Ralph Borelli said the pain of shingles was like an electric shock going down his leg repeatedly. (CBC)

Merck's TV ad for Zostavax says it is indicated to prevent shingles in people age 50 or older. The viral flare-up is portrayed as flashes lighting up across the hip and chest.

CBC News asked Dr. Shelly McNeil at the Canadian Center for Vaccinology in Halifax to analyze the manufacturer's claims. A limitation of giving the vaccine for people in their 50s is that might be too early, said McNeil, a professor of medicine at Dalhousie University and a member of the National Advisory Committee on Immunization (NACI).

"We know that it lasts out to about five years for sure, but my main risk of course will be when I'm 70, 80, 90," McNeil said.

"The earlier we give it, the higher the chance perhaps that it may not still be working by the time you're at your highest period of risk."

Doctors need to decide what age of patients they should offer the vaccine to, given it costs about $200 and isn't covered by provincial health insurance plans.

The vaccine's effectiveness varies with age. (Jim Cole/Associated Press)

Anyone trying to decide also faces a paradox: advancing age increases the likelihood of getting shingles itself but the effectiveness of the vaccine also decreases with age.

According to the drug company's own research:

• The vaccine cuts the risk of illness by half for those in their 60s.
• Between the ages of 70 to 79, the effectiveness falls to 41 per cent.
• For those 80 years and older, the effectiveness is less than 20 per cent.

The national advisory committee's recommendations for the vaccine include:

• It is recommended for the prevention of herpes zoster and its complications in persons 60 years and older without contra-indications.
• Administer the vaccine regardless of prior history of chickenpox or documented infection.
• Booster shots are not recommended for healthy individuals.
• May be used in people age 50 and older.

McNeil pointed to the real problem of long-term pain complication that can happen in up to half of those over the age of 70. It's debilitating, very difficult and expensive to treat.

That's why McNeil believes Zostavax works well enough for provincial health plans to implement a publicly funded vaccination program.

She's studying a live version of the vaccine containing a weakened form of the virus for people whose immune systems don't work normally, such as people with organ transplants or cancer.

Ralph Borelli, 61, knows how painful shingles is. In 35 years on the job, Borelli said he hadn't missed a day of work. That was until Christmas time, when he could no longer walk, lie down or stand up from the painful rash on his leg, hip and foot.

"What I can tell you is that it's been the most painful experience I've ever had," said Borelli, likening it to an electric shock going down his leg a few times a day. He's still getting pain two months later.

"If it prevents the pain, it's worth it," Borelli said. He's planning to ask his doctor for the vaccination to avoid experiencing it again.

With files from CBC's Kim Brunhuber and Laura MacNaughton