Preventing varicella: Recommendations for routine two-dose varicella immunization in children

Question 1

What is primary vaccine failure?

Answer 1

after vaccine is given, a protective immune response does not develop.

Question 2

What is secondary vaccine failure?

Answer 2

Waning immunity

Question 3

When should the second dose of the varicella vaccine be given?

Answer 3

4-6yo, minimum dose interval q3m if children <12yo

Question 4

What are the recommendations re: prenatal assessment for varicella immunity?

Answer 4

1. Prenatal assessment of women for evidence of varicella immunity
2. Vaccinate those who are non-immune after completion of pregnancy

Question 5

What shows evidence of immunity to varicella?

Answer 5

1. IgG to VZV as measured by any method (confirms natural disease)
2. documentation of receipt of two doses of varicella vaccine (do not do serology)
3. laboratory confirmation of varicella or herpes zoster from a lesion
4. previous diagnosis of varicella disease or herpes zoster by a health care provider.

Question 6

What are the CPS recommendations?

Answer 6

1. Healthy children aged 12 months to 12 years of age should receive two doses of varicella-containing vaccine for primary immunization (A-III). The second dose of varicella vaccine may be given three months or longer after the first varicella immunization. The second dose should be given at four to six years of age in order to minimize risk of infection resulting from waning immunity, or until all provinces and territories have universal programs in place, or until more data are available on the best scheduling option.
2. The first dose of a varicella-containing vaccine should be given between 12 and 18 months of age.
3. Susceptible adolescents 13 years of age and older should continue to receive two doses of varicella vaccine four weeks apart.
4. Children who have received one dose of varicella vaccine should be immunized with a second dose if they have not developed breakthrough disease.
5. Canadian physicians should advocate for universal funding and integration of this two-dose regimen into provincial and territorial programs to ensure equitable access for all Canadian children.
6. Prenatal assessment of women for evidence of varicella immunity (criteria in text) is recommended. Women who do not have evidence of varicella immunity should be vaccinated once they are no longer pregnant.
7. Further research should be done in Canada to determine:
   a) Duration of vaccine-induced varicella immunity, and requirements for future boosters
   b) Relative contributions of primary and secondary vaccine failure
   c) Optimal spacing of the two doses
   d) Varicella surveillance and vaccine coverage rates in Canada.