Hepatitis A+B Combined

Travelers to endemic areas, people at risk for both hepatitis A and B.

Severe allergic reaction (anaphylaxis) to a previous dose of Twinrix, or to any hepatitis A or hepatitis B vaccine, or to any component including yeast and neomycin. Moderate to severe acute illness (defer until recovery).

Very common (≥1/10): injection site pain and redness (35–41%), headache (22%), fatigue (18%). Common (1–10%): injection site swelling, fever, malaise, nausea, diarrhea, myalgia. Serious adverse events are extremely rare. Safety profile is consistent with that of monovalent hepatitis A and hepatitis B vaccines individually.

Standard schedule: 3 doses IM at 0, 1, and 6 months (same as hepatitis B). Accelerated schedule: 4 doses at 0, 7, 21–30 days + booster at 12 months (for travelers with insufficient time for standard schedule). Dose: 1.0 mL intramuscular in deltoid. Pediatric formulation (Twinrix Junior): 0.5 mL, ages 1–15 years. Store at +2°C to +8°C, do not freeze.

Anti-HAV seroconversion: 93.8% after dose 1, 98.8% after dose 2, 99.9% after dose 3. Anti-HBs seroprotection (≥10 mIU/mL): 30.8% after dose 1, 78.2% after dose 2, 98.5% after dose 3. Accelerated schedule: 82% anti-HBs seroprotection at day 28 (after 3 doses), rising to 98.5% after booster at 12 months. Long-term protection: comparable to monovalent vaccines (HAV: ≥25 years, HBV: ≥30 years estimated).

Can be co-administered with most travel vaccines (yellow fever, typhoid, meningococcal, rabies) at different injection sites. Immunoglobulins (HAV IG or HBIG) may be given at a separate site if immediate post-exposure protection is needed, though anti-HAV titers may be slightly reduced. No known clinically significant drug interactions.

Pregnancy: Twinrix® (inactivated hepatitis A + recombinant hepatitis B) has limited data in pregnancy. Both individual components (hepatitis A and hepatitis B vaccines) have established safety profiles in pregnancy. Hepatitis B vaccination is routinely recommended for pregnant women at risk of HBV infection. Hepatitis A vaccine may be administered during pregnancy when indicated. The theoretical risk from inactivated vaccines during pregnancy is negligible. Consider Twinrix® if both hepatitis A and B protection are needed and the travel timeline is tight.

Breastfeeding: Twinrix® (inactivated) is compatible with breastfeeding. Both hepatitis A and hepatitis B vaccines are inactivated and pose no risk to the breastfed infant. Inactivated vaccines do not replicate and cannot be transmitted through breast milk. No modification of breastfeeding schedule is required. Vaccination of breastfeeding mothers who require hepatitis A and/or B protection should not be deferred.

Pediatric use: Twinrix® is approved for individuals ≥18 years in the United States. A pediatric/adolescent formulation (Twinrix Junior®) is available in some markets for children aged 1–15 years. For children under the approved age, individual hepatitis A and hepatitis B vaccines should be administered separately. Hepatitis A vaccine is recommended from 12 months of age; hepatitis B vaccine is given as part of the routine birth dose series. Children traveling internationally should ideally complete both vaccine series before travel.

Older adults (≥65 years): Twinrix® can be administered to older adults. Immune response to both hepatitis A and hepatitis B components may be diminished in older adults due to immunosenescence. For hepatitis B specifically, seroconversion rates decline with age (approximately 75% in adults ≥60 vs >95% in young adults). Post-vaccination serological testing (anti-HBs) may be considered for older adults at ongoing risk. A higher-dose hepatitis B vaccine (Heplisav-B®) may be used separately if enhanced HBV response is desired.

Safe in pregnancy when indicated (inactivated vaccine). Safe in breastfeeding. Immunocompromised patients may have reduced response — consider checking anti-HBs titers after completion. Not a substitute for post-exposure prophylaxis when immediate protection is needed (use monovalent + immunoglobulin). Persons already immune to one component can still safely receive the combination.