Is a univalent Varicella vaccine recommended for a 21-year-old patient in Canada with only one dose of Measles, Mumps, Rubella, and Varicella (MMRV) vaccine?

Varicella Vaccination for a 21-Year-Old with One Prior MMRV Dose

Yes, a second dose of univalent varicella vaccine is recommended for this 21-year-old patient who has only received one dose of MMRV vaccine previously. 1

Rationale for Second Dose

The Advisory Committee on Immunization Practices (ACIP) clearly recommends that persons aged >13 years without evidence of varicella immunity should receive two doses of varicella vaccine. A single dose of varicella vaccine does not constitute evidence of immunity. 1

Key points supporting this recommendation:

• Persons aged >13 years should receive two 0.5-mL doses of single-antigen varicella vaccine administered subcutaneously, 4-8 weeks apart
• Only single-antigen varicella vaccine (not MMRV) is licensed for use in persons aged >13 years
• For individuals who previously received only one dose of varicella vaccine, a second dose is necessary to provide evidence of immunity 1

Vaccination Schedule for This Patient

For this 21-year-old patient:

1. Administer one dose of univalent (single-antigen) varicella vaccine now
2. The minimum interval between doses for persons aged >13 years is 4 weeks 1
3. If >8 weeks elapse after the first dose, the second dose may still be administered without restarting the schedule 1

Evidence Supporting Two-Dose Recommendation

The two-dose recommendation is based on several important findings:

• Vaccine effectiveness after one dose is only about 85%, which has not been sufficient to prevent varicella outbreaks 1
• Breakthrough varicella can occur in individuals who received only one dose
• Studies demonstrate a greater-than-tenfold boost in antibody titers after a second dose 2
• Two doses provide significantly higher protection (94.9% efficacy against all varicella and 99.5% against moderate to severe disease) compared to one dose (65.4% efficacy against all varicella) 3
• Primary vaccine failure appears to be a more significant issue than waning immunity (secondary vaccine failure) 4

Special Considerations for College Students

This recommendation is particularly important for this 21-year-old patient because:

• College students are specifically identified as a high-risk group for varicella transmission due to high contact rates 1
• All students in postsecondary educational institutions should be assessed for varicella immunity, and those without evidence of immunity should receive 2 doses of varicella vaccine 1
• Varicella disease is more severe and complications are more frequent among adolescents and adults compared to children 1

Documentation of Immunity

According to guidelines, evidence of immunity to varicella includes any of the following:

1. Documentation of 2 appropriately timed doses of varicella vaccine
2. Laboratory evidence of immunity or laboratory confirmation of disease
3. Birth in the U.S. before 1980 (except for healthcare workers and pregnant women)
4. Healthcare provider diagnosis or verification of varicella disease
5. Healthcare provider diagnosis or verification of herpes zoster 1

Since this patient has only received one dose of MMRV vaccine, they do not meet the criteria for evidence of immunity.

Practical Considerations

• Only univalent varicella vaccine should be used (not MMRV) as MMRV is not licensed for use in persons aged >13 years 1
• Serologic testing before vaccination is generally not recommended unless it's cost-effective (such as for healthcare workers) 5
• Standard commercial assays may sometimes fail to detect vaccine-induced immunity despite actual protection 5

By completing the two-dose varicella vaccination series, this patient will achieve optimal protection against varicella infection and its complications.