Efficacy of Single-Dose Shingles Vaccine
A single dose of Shingrix provides only 56.9% effectiveness against herpes zoster, which is substantially inferior to the 70.1% effectiveness achieved with the complete two-dose series—therefore, completing both doses is essential for optimal protection. 1
Two-Dose Series: The Evidence-Based Standard
The FDA-approved regimen for Shingrix requires two doses administered 2-6 months apart, based on pivotal clinical trials that demonstrated this schedule's superior efficacy 2, 3:
- Two-dose efficacy: 97.2% in adults aged ≥50 years (ZOE-50 trial) 2, 3
- Two-dose efficacy: 89.8% in adults aged ≥70 years (ZOE-70 trial) 2, 3
- Single-dose effectiveness: 56.9% in real-world Medicare data—a 13.2 percentage point reduction compared to two doses 1
Real-World Performance Gap
The most robust post-licensure data comes from a large Medicare cohort study examining real-world effectiveness 1:
- Two-dose vaccine effectiveness: 70.1% (95% CI: 68.6-71.5) against herpes zoster 1
- Single-dose vaccine effectiveness: 56.9% (95% CI: 55.0-58.8) against herpes zoster 1
- Two-dose effectiveness against postherpetic neuralgia: 76.0% (95% CI: 68.4-81.8) 1
These real-world effectiveness estimates are lower than clinical trial efficacy because real-world studies capture less specific outcomes and include broader populations, but the pattern is clear: incomplete vaccination leaves patients substantially less protected 1.
Critical Timing Considerations
The second dose can be administered beyond the recommended 2-6 month window without compromising effectiveness 1:
- Second doses given at ≥180 days (6 months) maintained full effectiveness with no significant decline 1
- The minimum interval between doses is 4 weeks; if given earlier, the dose should be repeated 2
- For immunocompromised adults aged ≥18 years, a shortened schedule with the second dose at 1-2 months is recommended 2, 4
Completion Rates in Practice
Real-world uptake data from October 2017 to September 2019 shows 5:
- 70% of patients completed the two-dose series within 6 months of the first dose 5
- 80% completed the series within 12 months of the first dose 5
- This means 20-30% of patients remain inadequately protected due to incomplete vaccination 5
Comparison to Zostavax (Live-Attenuated Vaccine)
The older live-attenuated vaccine (Zostavax) demonstrates why single-dose strategies are problematic 6, 7:
- Zostavax initial efficacy: 46-70% (already lower than Shingrix two-dose) 2
- Zostavax efficacy by year 10: only 14.1%—demonstrating rapid waning 2
- Zostavax efficacy in adults ≥80 years: only 18% 2
Shingrix's two-dose regimen was specifically designed to overcome the limitations of single-dose live vaccines 2.
Duration of Protection with Complete Series
With the full two-dose series, Shingrix provides durable protection 2:
- Protection maintained above 83.3% for at least 8 years 2, 8
- Efficacy at year 4: 93.1% (95% CI: 81.3-98.2) 3
- No booster doses beyond the initial two-dose series are currently recommended 2
Common Pitfall to Avoid
Do not consider a single dose "adequate" vaccination—patients who receive only one dose should be counseled that they have incomplete protection and strongly encouraged to complete the series 2, 1. The 13-point effectiveness gap between one and two doses translates to thousands of preventable shingles cases annually 1.
Special Populations
Even in challenging populations, the two-dose series remains superior 1:
- Two-dose effectiveness was maintained in adults aged >80 years 1
- Two-dose effectiveness was maintained in patients with autoimmune conditions 1
- Two-dose effectiveness was maintained in immunosuppressed individuals 1
For immunocompromised adults aged ≥18 years, Shingrix is the only appropriate vaccine (Zostavax is contraindicated), and completing both doses remains essential despite potentially reduced immune response 2, 4.