Chicken pox has been a rite of passage for generations of children, but these days it's uncommon for kids to come down with the blistering rash and fever symptomatic of the disease. That's because for decades in North America, and since 2003 in Nova Scotia, public health officials have provided chicken pox vaccinations to children after their first birthday.
However, as Joanne Weiss Reid found out just before Christmas, even with the vaccine, kids can still get sick. Weiss Reid's two children, aged three and six, both came down with chicken pox despite having been vaccinated at about 18 months of age. And it wasn't just her two kids. The children of friends who had visited during the contagious stage of the disease both came down with chicken pox, and both had already been vaccinated.
"Everyone I know who’s had the chicken pox has had the vaccine as well," says Laura Simpson, a neighbour of Weiss Reid. Simpson's 17-month old daughter came down with a mild case of chicken pox despite having already been vaccinated.
Contrary to common belief, a dose of chicken pox vaccine doesn't ensure your child won't get the disease. That’s because it wasn’t designed to give total immunity, according to the Canadian Paediatric Society's Dr. Marina Salvadori. The goal of the vaccine was not to eliminate the disease, but rather to prevent severe complications---including flesh eating disease, pneumonia, and other infections - that were occurring in some cases. “Even though it was a disease that almost every child got, there was a small group with really severe complications,” says Salvadori. And so in the U.S. and Canada, as well as in most other developed countries, public health officials started giving single dose vaccinations to kids over a year old. “The program has had excellent results,” says Salvadori. “Now we almost never see hospitalizations and severe complications from chicken pox.”
But it seems the vaccine program is a victim of its own success. The single dose vaccine leaves about 15 precent of people open to getting chicken pox---though a milder version---thanks to vaccine exposure. And with so little chicken pox around, the average age of the infection for that remaining 15% started to climb. “We saw the average age, if you were going to get it, move from 4 to 6 years up to 16 to 18 years,” says Salvadori. And because chicken pox has always been more severe in older children or adults, Salvadori and the Canadian Paediatric Society are now recommending a two dose system.
Salvadori is clear that the virus is not altering itself or beating the vaccine. “The virus is not getting stronger,” says Salvadori. “It's exactly the same virus. But if you get only one dose in early childhood, your immunity probably does wane over time.”
“We used to get exposed all the time and get natural boosting,” says Salvadori. “But now that we've almost gotten rid of the disease, you don't actually get enough natural boosting. So you need to get a second booster dose.”
Nova Scotia provides just a single dose, though some provinces in Canada have moved to two doses, though administered at varying ages. In the US, a national two-dose system has been in place for years. “This is actually a fundamental problem in Canada, says Salvadori. “We're really the only developed country in the world that doesn't do things on a national level, because of the way our health system is set up.”
Though the single dose vaccine didn’t prevent Joanne Weiss Reid’s children from getting chicken pox, it likely meant a milder case of the disease for them. “It actually turned out well," says Weiss Reid. “If they were going to get it, I'm glad they got it now. Both doctors we saw said that they would have had a much more severe case had they not been vaccinated.”
