Can you get the influenza (flu) vaccine when you're already sick?

Flu Vaccination During Illness

Yes, you can get the flu vaccine when you have a minor illness, but you should wait until symptoms resolve if you have a moderate to severe febrile illness.

Vaccination Guidelines for Minor vs. Severe Illness

Minor Illnesses

• Minor illnesses with or without fever do NOT contraindicate the use of influenza vaccine 1, 2
• This includes:
  • Mild upper respiratory tract infections
  • Allergic rhinitis (hay fever)
  • Common cold symptoms
  • Low-grade fever

When to Delay Vaccination

• Persons with acute febrile illness usually should not be vaccinated until their symptoms have abated 1
• Vaccination should be deferred in cases of:
  • Moderate to severe febrile illness
  • High fever
  • Active infection requiring hospitalization

Evidence-Based Rationale

The Advisory Committee on Immunization Practices (ACIP) has consistently maintained that minor illnesses should not prevent vaccination 1. This recommendation has remained consistent through decades of guidelines, with the most recent guidelines continuing to support this approach 1.

According to the American Academy of Pediatrics, "Minor illnesses, with or without fever, are not contraindications to the use of influenza vaccines, including among children with mild upper respiratory infection symptoms or allergic rhinitis" 1.

Special Considerations

For Children

• Children with mild upper respiratory symptoms can safely receive the flu vaccine 1
• For children with nasal congestion that would impede delivery of the live attenuated influenza vaccine (LAIV), the inactivated vaccine (IIV) may be used instead, or LAIV can be deferred until resolution 1

For Adults

• Adults with minor illnesses can safely receive the flu vaccine without waiting for symptoms to resolve 2
• The presence of mild symptoms does not affect the immune response to vaccination 2

Potential Concerns

Differentiating Vaccine Side Effects from Illness

• Common side effects of flu vaccination include:
  • Soreness at injection site
  • Low-grade fever
  • Muscle aches
• These symptoms can sometimes be difficult to distinguish from the original illness

COVID-19 Considerations

• For persons with COVID-19, vaccination should usually be deferred until they have recovered 1
• For those with moderate or severe COVID-19, deferral is recommended
• For mild or asymptomatic COVID-19, further deferral might be considered to avoid confusing COVID-19 symptoms with post-vaccination reactions 1

Clinical Decision Algorithm

1. Assess severity of current illness:

   • Minor illness (mild symptoms, with or without low-grade fever) → Proceed with vaccination
   • Moderate to severe illness (high fever, significant symptoms) → Defer vaccination until symptoms resolve

2. Consider type of vaccine if nasal congestion is present:

   • If using LAIV (nasal spray) and significant nasal congestion exists → Consider using injectable vaccine instead or defer LAIV

3. For COVID-19 positive patients:

   • Moderate/severe COVID-19 → Defer vaccination until recovered
   • Mild/asymptomatic COVID-19 → Consider deferring to avoid symptom confusion

Remember that timely vaccination against influenza is important for protection, and minor illnesses should not be a barrier to receiving this important preventive measure.