Should children on treatment for atypical Hemolytic Uremic Syndrome (aHUS) receive the yearly influenza vaccine?

Influenza Vaccination in Children with Atypical Hemolytic Uremic Syndrome (aHUS)

Children on treatment for atypical hemolytic uremic syndrome (aHUS) should receive the yearly influenza vaccine as part of their routine preventive care. 1

Rationale for Influenza Vaccination in aHUS Patients

Risk Assessment

• Children with aHUS are considered immunocompromised and at higher risk for complications from influenza infection
• Influenza infections can trigger aHUS episodes in susceptible individuals 2, 3
• Influenza B has been documented as a trigger for aHUS in patients with underlying genetic complement dysregulation 2
• Influenza A (H1N1) has also been reported to trigger aHUS in patients with mutations in complement regulatory genes 3

Vaccination Recommendations

The American Academy of Pediatrics (AAP) specifically recommends annual influenza vaccination for:

• All children 6 months and older, with special emphasis on those with chronic medical conditions 1
• Children with immunosuppression or chronic medical conditions that increase the risk of influenza complications 1

Benefits of Influenza Vaccination in aHUS Patients

1. Prevention of aHUS Triggers:

   • Influenza infection can trigger complement activation and precipitate aHUS episodes
   • Vaccination may prevent these triggering events 2

2. Reduced Morbidity and Mortality:

   • Preventing influenza reduces risk of hospitalization and complications
   • Children younger than 2 years are at increased risk of hospitalization from influenza 1
   • Historically, 80-85% of pediatric influenza deaths occur in unvaccinated children 1

3. Community Protection:

   • Reducing influenza transmission among children decreases burden on household contacts and community members 1

Safety Considerations

While there are limited studies specifically on influenza vaccination in aHUS patients:

• Influenza vaccines are generally safe in immunocompromised patients 4
• The risk of vaccine-induced complement activation appears to be low
• A case series of COVID-19 vaccination in aHUS patients showed that among 29 aHUS patients who received a total of 73 COVID-19 vaccinations, none developed aHUS relapse 5
• The benefits of preventing influenza (a known trigger for aHUS) outweigh the theoretical risks of vaccination

Practical Recommendations

1. Vaccination Timing:

   • Provide annual influenza vaccination at the start of influenza season
   • For children on eculizumab therapy, coordinate vaccination timing with treatment schedule

2. Monitoring After Vaccination:

   • Monitor for signs of complement activation or aHUS relapse after vaccination
   • Consider checking serum creatinine, proteinuria, hemolysis parameters, and blood pressure days after vaccination 5

3. Patient/Family Education:

   • Educate families about potential symptoms of aHUS relapse that should prompt medical attention
   • Emphasize the importance of annual vaccination despite the small theoretical risk

Special Considerations

• For children on eculizumab therapy, remember that meningococcal vaccination is also required, though this may not be possible in very young infants 6
• In children under eculizumab treatment too young for meningococcal vaccination, prophylactic antibiotics may be needed 6

Conclusion

The evidence strongly supports providing yearly influenza vaccination to children with aHUS. The risk of influenza infection triggering an aHUS episode is greater than the theoretical risk of the vaccine causing a relapse. The American Academy of Pediatrics guidelines specifically recommend vaccination for immunocompromised children and those with chronic medical conditions, which includes patients with aHUS.