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Chicken pox is one of those childhood illnesses that never really lets go.

Once the initial infection has passed, the bug responsible - the varicella-zoster virus - goes dormant and takes up permanent residence in certain nerves.

If your immune system weakens, especially as you age, the virus can reactivate to produce a painful, unsightly rash with fluid-filled blisters known as shingles. What's worse, the pain can linger for months, even years, after the rash and blisters have healed, a condition known as postherpetic neuralgia.

Now, however, a new vaccine is available to keep this nasty virus under wraps. Merck Frosst has won Health Canada's approval to market the vaccine, called Zostavax, to those 60 and older. It has been sold in the United States since May, 2006.

"I would anticipate that a lot of people are going to want to get this vaccine," said Shelly McNeil, a vaccine researcher and adult-infectious-disease specialist at the Queen Elizabeth II Health Sciences Centre in Halifax.

Each year, about 130,000 Canadians suffer a bout of shingles, most of them older individuals. About 20 per cent of us eventually will be stricken, Dr. McNeil said.

Zostavax is made with a live attenuated - or "weakened" - virus that can prompt the immune system to boost its defences against the bug without causing the illness. The vaccine must be stored at -15 C to keep the virus alive. That will likely limit the number of family physicians initially offering the shots because their offices lack proper refrigeration facilities.

The vaccine isn't 100-per-cent effective. Studies in people over 60 suggest it cuts the chances of developing shingles by 50 per cent. But if you do get shingles after receiving the shot, it tends to be a milder outbreak. "The real benefit of this vaccine is likely to be a reduction of the long-term pain from postherpetic neuralgia," Dr. McNeil said.

The vaccine isn't cheap. The company has set a list price of $150. (The cost could be somewhat higher for patients.) None of the provinces currently intend to foot that bill as part of their publicly funded vaccinations programs, although some private health-insurance plans may cover it.

"It's not a small amount of money, but if you talk to people who have had shingles, most of them would try to cough up $150 so it doesn't happen to them again," Dr. McNeil said.