Children should receive two doses of chickenpox vaccine, Canadian pediatricians say.

The Canadian Pediatric Society (CPS) updated its position statement on chickenpox or varicella vaccination on Tuesday.

Chickenpox is an infectious disease that results in a blister-like rash, itching, tiredness, and fever. (Dr. John Noble, Jr./CDC)

Without a second dose, there is evidence that some children will lose immunity as they get older and will be at risk of illness as an adult, said Dr. Marina Salvadori, the statement's author.

Since 1999, the group has recommended that all Canadian children be vaccinated against chickenpox. By 2007, all Canadian provinces and territories had routine immunizations programs consisting of one dose of the vaccine.

Canada's goal, set in 2005, was to reduce incidence of chickenpox by 90 per cent by 2015 and to reduce chickenpox-related hospitalizations and deaths by 80 per cent by 2010.

Pediatric hospital surveillance data suggests Canada is approaching its goal.

The immune system can handle thousands of challenges a day, said Salvadori.

"This is actually a very tiny number of challenges with this vaccine. We know that your body can easily handle the number of vaccines that children get," she said in an interview from London, Ont.

For parents who are concerned about the number of shots their children get, Salvadori said some immunizations are now combined so kids aren't necessarily getting more needles.

Data from the U.S. suggests the average age of those who get chickenpox is increasing among those vaccinated with one dose and those who were never vaccinated, the position statement said.

The new guideline says:

• Children get their first dose of the vaccine between 12 and 18 months, and should receive the booster dose when they are four to six years old.
• Teens who have never had chickenpox should get two shots, at least four weeks apart.
• Varicella immunity should be assessed prenatally, and women without evidence of the immunity should be vaccinated once they are no longer pregnant.

The pediatricians called for more research such as on how long the immunity lasts and what is the best spacing of the two doses.