Study finds huge drop in chickenpox cases after Ontario began public vaccine program

TORONTO -- Ontario's publicly funded chickenpox vaccination program appears to have dramatically reduced the number of children who get infected with the virus, researchers say.

In a study that looked at 20 years of data, Public Health Ontario found a 71 per cent drop in doctor's office and emergency room visits and a 59 per cent decrease in hospitalizations due to chickenpox among children under 18 after the public immunization program was introduced in 2004, compared with two earlier periods.

Those time frames captured in the study were 1992 to 1998, when there was no vaccine, and 1999 to 2003, when the shot was available but had to be paid for out of parents' pockets.

"This is a vaccine program that very clearly is working," said lead author Dr. Anne Wormsbecker, a pediatrician and epidemiologist at Public Health Ontario.

"So it looks like from our study that kids are not getting as much chickenpox ... and fewer kids are being hospitalized for complications of chickenpox.

"So that's really a good news story."

Chickenpox is a highly contagious illness caused by the varicella zoster virus, which produces an itchy, blister-like rash and lasts about five to 10 days. Other symptoms include fever, fatigue and headache.

The virus spreads in the air when an infected person coughs or sneezes, but can also be contracted by touching or breathing in the virus particles from chickenpox blisters, according to the U.S. Centers for Disease Control.

"Chickenpox is usually a mild, self-limiting illness," said Wormsbecker.

"However, chickenpox in some cases -- and we can't predict in which cases -- can result in very serious complications, including infections of the skin and deeper tissues, the most serious being necrotizing fasciitis."

Those skin and tissue infections are caused by different types of bacteria, likely introduced when a child scratches a blister, she said.

Necrotizing fasciitis, or flesh-eating disease, is a potentially life-threatening infection caused by the group A streptococcus bacterium and can be severe enough to require surgery or, in some cases, limb amputation.

But the virus itself can also cause complications, by infecting the lungs, brain or bloodstream and organs, resulting in disability or death in rare cases.

"So that to me is a reminder that it's important to have the chickenpox vaccine, and I'm really happy to see that our vaccine is working," said Wormsbecker.

The study, published online Wednesday in the journal PLOS ONE, showed that between 1992 and 2011, there were more than 600,000 physician office visits, 55,500 emergency department visits and 2,700 hospitalizations for chickenpox among Ontario children.

In 1994, before the vaccine became available, visits to doctors' offices due to chickenpox were 25 per 1,000 children. In 2011, seven years after the publicly funded varicella vaccination program began, that figure dropped to 3.2 per 1,000 children.

The rates of hospital ER visits and hospitalizations saw similar declines, and chickenpox-associated skin and soft tissue infections declined significantly, especially in kids under 12.

Initially, children were given one dose of the varicella vaccine. But in 2011, doctors began administering two shots -- at 15 months old and between age four and six -- after research showed the double-dose regimen was better at preventing outbreaks in schools and other settings where groups of children come in close contact.