Infant varicella vaccination has been part of the New Brunswick schedule for six years. The vaccine has been given at 12 months of age with MMR vaccine.
At the time of introducing the vaccine there were a number of concerns about the impact of the program including:
- There were a high number of varicella cases reported among vaccinees in efficacy trials;
- Vaccination could lead to a shift in the age at infection from children to adults with more severe disease;
- The impact of immunization on herpes zoster was unknown;
- Studies suggested that ongoing subclinical infection with varicella could reduce the risk of herpes zoster by boosting specific immunity to VZV; and,
- If boosting occurs, reducing varicella infection through mass varicella vaccination will lead to an increase in herpes zoster.
Since introducing the vaccine post licensure studies have confirmed that:
- One dose of vaccine is 80-85% effective against any disease presentation although breakthrough varicella is generally mild and less contagious than varicella in unvaccinated persons;
- The age of cases is increasing as predicted;
- Protection afforded by one dose of vaccine wanes with time;
- Herpes zoster is increasing in areas with high varicella vaccine coverage in those who are unimmunized; and,
- Efficacy of 2 doses of varicella vaccination is significantly higher than 1 dose.
In view of this information the US Advisory Committee on Immunization Practices (ACIP) has recommended a second dose of varicella vaccination at 4-6 years of age and the Canadian National Advisory Committee on Immunization (NACI) now recommends that:
“A two dose varicella regime be implemented with the first dose of MMRV administered at 12-15 months, and the second at 18 months- or at 4-6 years-of-age (preschool). The doses may be administered closer together, with a minimum interval of 28 days (4 weeks) between doses.”
While some soft data exists to suggest that a second dose at 4-6 years may be more cost-effective than at 18 months, this needs to be balanced against the local schedule and the opportunities for consolidation.
In view of this NB is moving to a two dose varicella vaccine schedule at 12 months and 18 months commencing January 1 2011.
All children born after January 1st 2010 will commence the two dose schedule.
A catch up program for children born in 2009 will be available. All children born in 2009 may receive a publicly funded second dose of varicella vaccine either at the 18 month visit or anytime they are seen, so long as 28 days have passed since the first dose of vaccine. This can be accessed where they normally access the publicly funded immunization program.
A vaccine is available that combines MMR vaccine and varicella vaccine. This combination had been under a safety cloud because of the suggestion in US studies that the combined vaccine was associated with increased fevers and increased febrile convulsions of the order of 1:2500 doses when compared to the two vaccines given separately.
The vaccine used in Canada is not the same as that in the US and NACI have not cautioned against the local vaccine for which there are no safety signals. Additionally, data from Quebec where the local combined MMRV vaccine (Priorix-Tetra™) has been in use, has identified no increase in fever in that province.
In view of this NB is moving to the use of combined MMRV vaccines in its schedule as soon as sufficient MMRV stocks are available after January 1 2011. Combination vaccine may not be available until April.
This will enable the number of needles required at the 12 month visit to reduce to three again.
Please continue to use separate MMR and V vaccines until you are out of stock. Combined vaccine will be distributed when available.
This and the previously communicated pertussis changes are the only ones occurring in 2011. I appreciate the support the communicable disease team gets from its primary care partners.
Dr. Paul Van Buynder
Deputy Medical Officer of Health
December 10, 2010