In a typical adult without contraindications, can hepatitis A vaccine be given one week after an erroneous Engerix B (hepatitis B) dose that was given instead of the second dose of Twinrix (combined hepatitis A and B vaccine)?

Hepatitis A Vaccine Administration After Erroneous Engerix-B Dose

Yes, you can administer the hepatitis A vaccine one week after the erroneous Engerix-B dose without any waiting period, and you should continue the Twinrix series by counting the Engerix-B dose as a valid hepatitis B component. 1

Immediate Management Strategy

Give the hepatitis A vaccine (monovalent) immediately—there is no minimum interval required after the Engerix-B dose. The CDC explicitly states that when a dosing error occurs, the correct vaccine should be administered as soon as the error is identified, with no mandatory waiting period. 1 One week is more than sufficient, though you could have given it the same day.

Series Continuation Without Restart

Never restart the Twinrix series after this error; simply continue the series using the proper vaccines. 1, 2, 3 The CDC emphasizes across all hepatitis B vaccination guidance that interrupted or mixed series should never be restarted regardless of the circumstances. 1, 2

How to Count the Doses:

• The Engerix-B dose counts as a valid hepatitis B component (dose #2 of the hepatitis B series) because it contains the correct adult dose of 20 μg hepatitis B surface antigen. 2
• The hepatitis A component is missing, so you need to provide monovalent hepatitis A vaccine to complete that portion. 1

Completing the Vaccination Series

After giving the monovalent hepatitis A vaccine now (at week 1 post-Engerix-B):

For Hepatitis B:

• Administer the third hepatitis B dose at least 8 weeks after the Engerix-B dose (dose #2) AND at least 16 weeks after the first Twinrix dose (dose #1). 1, 2 The preferred timing would be at month 6 from the original first Twinrix dose. 1
• You can use either Engerix-B or complete with a third Twinrix dose (which would provide an extra hepatitis A dose, but this is not harmful). 1, 4

For Hepatitis A:

• Administer the second hepatitis A dose at least 6 months after the first Twinrix dose. 5 Since the patient received one dose of hepatitis A antigen in the first Twinrix and you're now giving a monovalent hepatitis A vaccine, the second hepatitis A dose should follow the standard 0,6-month hepatitis A schedule. 5

Practical Algorithm

Week 0: First Twinrix dose (contains both hepatitis A and B)
Week 4: Engerix-B given in error (valid hepatitis B dose #2, but missing hepatitis A)
Week 5 (now): Give monovalent hepatitis A vaccine immediately
Month 6: Give third hepatitis B dose (Engerix-B or Twinrix) to complete hepatitis B series
Month 6: Ensure second hepatitis A dose is given (if not already included in a Twinrix dose at month 6)

Critical Pitfalls to Avoid

• Do not delay the hepatitis A vaccine waiting for a specific interval—there is no minimum waiting period after the Engerix-B error. 1
• Do not restart the entire Twinrix series—this wastes doses and delays protection. 1, 2, 3
• Do not give the third hepatitis B dose before 16 weeks from the first Twinrix dose, even if 8 weeks have passed since the Engerix-B dose. 1, 2
• Do not assume the patient needs four total doses of hepatitis B vaccine—three properly spaced doses are sufficient. 1, 2

Alternative Simplified Approach

If you prefer to avoid mixing monovalent and combination vaccines, you could:

• Give the monovalent hepatitis A vaccine now (week 5)
• Complete with Twinrix at month 6 (which provides both the third hepatitis B dose and second hepatitis A dose simultaneously)

This approach ensures complete protection against both viruses while maintaining proper intervals. 1, 6, 4