MMRV Vaccination at 6 Months of Age in Canada
The MMRV vaccine should not be given at 6 months of age to infants in Canada, as Canadian guidelines recommend a minimum age of 12 months for the first dose of measles, mumps, rubella, and varicella vaccines.
Canadian Immunization Guidelines for MMRV
The National Advisory Committee on Immunization (NACI) in Canada recommends:
- The first dose of measles-containing vaccines (including MMRV) should be administered at 12-15 months of age 1
- The minimum age for administering the first dose of MMRV vaccine is 12 months 2
- For infants younger than 6 months of age who are exposed to measles, immunoglobulin (Ig) is recommended rather than vaccination 1
Scientific Rationale for Age Recommendations
Maternal Antibody Interference
- Maternal antibodies against measles, mumps, rubella, and varicella typically persist in infants for several months after birth, potentially interfering with vaccine response 3
- By 6 months of age, many infants still have maternal antibodies that can neutralize vaccine viruses and reduce vaccine effectiveness
- Studies show that maternal antibodies against MMRV decrease rapidly but may still be present at 6 months of age in some infants 3
Immune Response Considerations
- Research demonstrates that seroconversion rates to measles, mumps, and rubella are significantly better (>95%) when vaccination occurs at 12 or 15 months compared to earlier ages (80% at 9 months) 4
- Vaccine failure is less frequent when administered at 12 months or later 4
- A Quebec study found that even among children who received two doses of measles vaccine, those who received their first dose at 12 months had a 3-4 fold higher risk of measles compared to those vaccinated at ≥15 months 5
Special Circumstances
In certain high-risk situations, alternative approaches may be considered:
- For infants 6-12 months of age exposed to measles, MMR (not MMRV) may be given within 72 hours of exposure as post-exposure prophylaxis 1
- However, this is considered an off-label use and would not count toward the routine two-dose schedule
- These infants would still need to receive two additional doses of measles-containing vaccine at the recommended ages (12-15 months and 4-6 years) 1
Administration Recommendations for MMRV
When administering MMRV at the appropriate age (≥12 months):
- For the first dose at age 12-47 months, separate MMR and varicella vaccines are generally preferred over MMRV due to a slightly increased risk of febrile seizures with MMRV 2
- For the first dose at age ≥48 months or the second dose at any age, MMRV is generally preferred over separate injections 2
- A personal or family history of seizures is a precaution for MMRV vaccine use 2
Conclusion
The MMRV vaccine should not be administered to 6-month-old infants in Canada. The optimal age for the first dose is 12-15 months, with evidence suggesting that administration at 15 months may provide even better protection than at 12 months. This timing balances the waning of maternal antibodies with the development of a robust immune response in the infant.