CTV News Staff
A new study is suggesting that children who've been vaccinated
against chicken pox may need a second dose to guarantee complete
protection from the disease.
The study, to be published Thursday in the New England Journal
of Medicine, cited several examples of outbreaks that infected
children who had been vaccinated for chicken pox, including a
day-care centre in New Hampshire where 16 of 25 children infected
had been previously been given a shot for chicken pox.
"They had some immunity, but it wasn't completely protective,"
said Dr. Karin Galil of the U.S. Centers for Disease Control and
Prevention, the study's lead author. "It stopped them from getting
a bad case of chicken pox but it didn't protect them from getting
infected with the chicken pox virus."
The varicella zoster virus causes an itchy, blister-like rash
that covers the head and trunk. It is accompanied by headache,
fever and tiredness. The disease is a simple annoyance for most
children, but those with a suppressed immune system can develop
serious complications.
About five or six children die from complications each year in
Canada.
The vaccines' effectiveness against chicken pox is supposed to
range between 77 per cent and 100 per cent but Galil found the
single dose was only effective in 44 per cent of cases.
"We are taking very seriously the possibility that we might not
have the right optimal vaccination level yet," said Galil. "And if
there's evidence that we need to change it, that will be a
priority."
The good news is that most children infected after receiving
the vaccine developed only mild symptoms, with one child in the
New Hampshire study being diagnosed with just a single blister.
In fact, doctors credit the vaccine with cutting the total
number of cases of the nasty disease across North America. In the
U.S., chicken pox cases have dropped 80 per cent since the vaccine
was introduced in 1995.
Health Canada says the rate of chicken pox per 100,000 people
had fallen to 135.69 in 1999 from 301.7 in 1993.
"Since we have been using chicken pox vaccine the number of
admissions to hospital for severe disease, the amount of chicken
pox in the community and the severity of that chicken pox have
decreased significantly," said Dr. Stanley Read of the Hospital
for Sick Children in Toronto.
In Canada, only Alberta, Prince Edward Island and the Northwest
Territories pay for its use. Nova Scotia announced Wednesday it
intends to vaccinate all babies against chicken pox before they
turn one year old.
Other provinces are considering bringing the vaccine under
their health coverage, but some doctors fear the study will prompt
some health ministries to opt away from paying for the vaccine
until more studies are completed.
"I hope it's not used by the government as ammunition to say we
don't know enough about it so we should not pay for it," said Dr.
Tony Barozzino of St. Michael's Hospital in Toronto. "There is
lots of evidence to say, if anything, we need to give more of it."
U.S. health authorities are pushing states to adopt mandatory
chicken pox vaccinations, saying the vaccine reduces the costs
related to the disease, including the costs of missed work,
school, and childcare.
Meanwhile, the are also concerns that the vaccine could result
in an increase in adult chicken pox and shingles, a disease linked
to the varicella zoster virus.
Because multiple exposures of chicken pox boost immunity
throughout their lives, people who suffered a bout of chicken pox
as a child almost never get it again as an adult. Also, between 10
and 20 per cent of people who had chicken pox as a child
eventually develop shingles as an adult.
Because of the vaccine, those who had it as a child will not be
exposed as often, potentially making adult chicken pox and
shingles more common.
Several U.S. studies are underway to detect any evidence of
faltering immunity associated with the varicella vaccine.
