In a patient with chronic plaque psoriasis receiving risankizumab (Skyrizi), is it acceptable to give only two doses of hepatitis B vaccine?

Two Doses of Hepatitis B Vaccine is Insufficient

No, giving only two doses of hepatitis B vaccine is not acceptable—patients on risankizumab require a complete 3-dose series (or 2-dose series with Heplisav-B) to ensure adequate protection against hepatitis B virus reactivation. 1

Why the Complete Series is Critical

Patients receiving immunosuppressive therapy, including biologics like risankizumab for psoriasis, are specifically identified as requiring pre-treatment hepatitis B screening and complete vaccination 1. The ACIP guidelines explicitly state that persons needing immunosuppression for rheumatologic or gastroenterologic disorders must receive the full hepatitis B vaccine series 1.

Standard Vaccination Schedules

For adults ≥18 years, the complete series options are 2:

• Engerix-B, Recombivax HB, or PreHevbrio: 3 doses at 0,1, and 6 months
• Heplisav-B: 2 doses at 0 and 1 month (this is the ONLY approved 2-dose regimen)
• Twinrix: 3 doses at 0,1, and 6 months (standard) or 4 doses accelerated schedule

Two doses of a 3-dose series does NOT constitute adequate vaccination and leaves the patient vulnerable to hepatitis B infection or reactivation.

What Happens with Interrupted Series

If a patient has received only 2 doses of a 3-dose series, the guidelines are clear 1:

• The series does NOT need to be restarted
• Give the third dose as soon as possible
• The final dose must be administered ≥8 weeks after the second dose and ≥16 weeks after the first dose
• Inadequate doses or incomplete series should be completed using the correct schedule

Post-Vaccination Testing is Essential

For immunocompromised patients (which includes those on biologics), you must 1, 3:

1. Complete the full vaccine series first
2. Test anti-HBs levels 1-2 months after the final dose
3. If anti-HBs <10 mIU/mL, administer a second complete 3-dose series
4. Retest 1-2 months after completing the second series

This is critical because immunocompromised patients have lower response rates to hepatitis B vaccination, and you need serologic confirmation of immunity 3.

Specific Considerations for Risankizumab Patients

Recent evidence confirms that IL-23 inhibitors like risankizumab carry a risk of hepatitis B reactivation 4, 5. A 2025 study found that among psoriasis patients on biologics (including risankizumab), 21% were at risk for HBV reactivation, and prophylaxis was essential to prevent reactivation 4.

The AAD-NPF guidelines for biologics in psoriasis explicitly recommend hepatitis B screening before initiating therapy 6, and this logically extends to ensuring complete vaccination in susceptible patients.

Common Pitfall to Avoid

Do not assume that 2 doses provides adequate protection. The only scenario where 2 doses is sufficient is:

• Heplisav-B specifically (2 doses at 0 and 1 month) 2
• Recombivax HB in adolescents aged 11-15 years (2 doses at 0 and 4-6 months) 2

For all other hepatitis B vaccines in adults, 3 doses are required for a complete series.

Practical Algorithm

1. Before starting risankizumab: Screen for HBsAg, anti-HBc, and anti-HBs 1
2. If susceptible (all markers negative):
   • Administer complete vaccine series (3 doses or 2 doses of Heplisav-B)
   • Can start first dose immediately while awaiting test results 1
3. If only 2 doses of a 3-dose series given: Complete the third dose before considering the patient adequately vaccinated
4. Test anti-HBs 1-2 months after final dose 3
5. If anti-HBs <10 mIU/mL: Give second complete 3-dose series and retest 3

Bottom line: Complete the full hepatitis B vaccine series—two doses of a three-dose regimen leaves your patient inadequately protected against a potentially serious complication of biologic therapy.