Twinrix Rapid Schedule Third Dose Timing When Day 21 is Missed
If you miss the 21-day mark for the third dose of Twinrix on the rapid schedule, administer it as soon as possible within the 21-30 day window, and if that window is also missed, give it immediately when the patient returns—the series does not need to be restarted. 1
Recommended Timing for the Delayed Third Dose
The ACIP guidelines explicitly state that the Twinrix accelerated schedule allows for the third dose to be given between 21-30 days after the first dose, not strictly on day 21. 1 This built-in flexibility means:
- If still within days 21-30: Administer the third dose at any point during this window 1
- If beyond day 30: Give the dose as soon as the patient is available—do not restart the series 1
Key Principles for Interrupted Schedules
The ACIP provides clear guidance that applies to all hepatitis B-containing vaccines, including Twinrix:
- Never restart the series when the schedule is interrupted 1, 2
- If only the third dose has been delayed, it should be administered as soon as possible 1
- The vaccine series maintains its validity regardless of delays between doses 1
Important Caveat About the 4-Day Grace Period
The standard 4-day grace period for early vaccine administration does NOT apply to the first three doses of Twinrix when using the accelerated 0,7,21-30 day, 12-month schedule. 1 This is a unique exception due to the accelerated nature of this schedule, so do not give doses early in an attempt to "catch up."
Completing the Series
Regardless of when the third dose is ultimately given:
- The fourth dose at 12 months remains essential for long-term protection 1, 2
- This booster dose should be given 12 months after the first dose, not adjusted based on when the third dose was administered 1
Clinical Context
The accelerated Twinrix schedule was designed specifically for individuals needing rapid protection (such as travelers or high-risk populations), and research demonstrates that even with the accelerated schedule, 63.2% achieve hepatitis B seroprotection by day 37 (after the third dose), with nearly 100% hepatitis A seroconversion. 3 The flexibility in the 21-30 day window for the third dose maintains this protective benefit while accommodating real-world scheduling challenges.