What are the guidelines for flu shots, including recommended age groups, priority populations, and vaccine options?

Flu Shot Guidelines

All persons aged ≥6 months without contraindications should receive annual influenza vaccination, with vaccination ideally occurring by the end of October, though vaccination should continue throughout the influenza season as long as vaccine is available. 1, 2

Universal Vaccination Recommendation

• The CDC recommends routine annual influenza vaccination for all persons aged ≥6 months who do not have contraindications. 1, 2
• Any licensed, age-appropriate vaccine formulation should be used for each recipient. 2
• All currently available seasonal influenza vaccines in the United States are quadrivalent, containing hemagglutinin from one influenza A(H1N1)pdm09 virus, one influenza A(H3N2) virus, one influenza B/Victoria lineage virus, and one influenza B/Yamagata lineage virus. 2

Priority Populations at Higher Risk

When vaccine supply is limited, prioritize these groups (no hierarchy implied): 1

• All children aged 6 through 59 months 1
• All persons aged ≥50 years 1
• Pregnant women at any trimester (only inactivated or recombinant vaccines, never live attenuated) 1, 3
• Adults and children with chronic conditions: pulmonary (including asthma), cardiovascular (excluding isolated hypertension), renal, hepatic, neurologic, hematologic, or metabolic disorders (including diabetes) 1
• Immunocompromised persons from any cause, including medication-induced or HIV infection 1
• Children and adolescents (6 months-18 years) receiving aspirin or salicylate-containing medications who might be at risk for Reye syndrome 1
• Residents of nursing homes and long-term care facilities 1
• American Indian or Alaska Native persons 1
• Persons with extreme obesity (BMI ≥40 for adults) 1

Healthcare Workers and Caregivers

All healthcare personnel should be vaccinated annually to protect themselves, their patients, and communities. 1

• This includes physicians, nurses, nursing assistants, nurse practitioners, physician assistants, therapists, technicians, emergency medical service personnel, dental personnel, pharmacists, laboratory personnel, students, trainees, and administrative staff. 1
• Vaccination of healthcare workers is associated with decreased mortality among nursing home patients. 1, 4
• Household contacts and caregivers of high-risk persons should also be vaccinated to prevent transmission. 1

Timing of Vaccination

For most persons requiring only one dose, vaccination should ideally occur during September or October. 2

• For adults aged ≥65 years and pregnant persons in first or second trimester: Avoid vaccination in July and August unless there is concern that later vaccination might not be possible. 2
• For children aged 6 months-8 years requiring 2 doses: Administer the first dose as soon as vaccine is available, including during July and August, to allow the second dose by end of October. 3, 2
• Vaccination should continue throughout the influenza season, even after influenza activity has begun, as vaccine administered in December or later can still be beneficial. 1
• Providers should offer vaccination to unvaccinated persons who have already had influenza during the season, as the vaccine might protect against other circulating strains. 1

Dosing Requirements by Age

Children Aged 6 Months Through 8 Years

Children in this age group require special attention to dosing schedules: 3, 2

• Two doses (separated by at least 4 weeks for inactivated vaccine or 6 weeks for live attenuated vaccine) are required if: 3
  • Receiving influenza vaccine for the first time, OR
  • Have not previously received at least 2 total doses of influenza vaccine before July 1 of the current season
• One dose is sufficient if: The child has previously received at least 2 total doses of influenza vaccine (separated by at least 4 weeks) before July 1 of the current season. 3

Children Aged 9 Years and Older, and Adults

• Only one dose per season is required, regardless of vaccination history. 3, 2

Vaccine Selection by Age

Children Aged 6-35 Months

• Dose volumes differ by product: Afluria Quadrivalent (0.25 mL), Fluarix Quadrivalent (0.5 mL), Flucelvax Quadrivalent (0.5 mL), FluLaval Quadrivalent (0.5 mL), Fluzone Quadrivalent (0.25 mL or 0.5 mL). 2

Children Aged 36 Months Through 17 Years

• All inactivated influenza vaccines are administered at 0.5 mL per dose. 2

Adults Aged ≥65 Years

Preferentially receive any one of the following enhanced vaccines: 2

• Quadrivalent high-dose inactivated influenza vaccine (HD-IIV4) - 0.7 mL per dose
• Quadrivalent recombinant influenza vaccine (RIV4) - 0.5 mL per dose
• Quadrivalent adjuvanted inactivated influenza vaccine (aIIV4) - 0.5 mL per dose

Route of Administration

• Inactivated vaccines: Administered intramuscularly in the deltoid muscle for adults and older children, or anterolateral thigh for infants and younger children. 2, 4
• Live attenuated vaccine (LAIV4): Administered intranasally and only approved for healthy persons aged 5-49 years. 1, 2

Contraindications

Do not administer inactivated influenza vaccine to persons with anaphylactic hypersensitivity to eggs or other vaccine components without first consulting a physician. 1

• Persons with acute febrile illness should not be vaccinated until symptoms have abated. 1, 4
• Minor illnesses with or without fever do not contraindicate vaccine use, particularly among children with mild upper respiratory infection or allergic rhinitis. 1, 4
• LAIV4 is contraindicated during pregnancy and in certain other populations including immunocompromised persons. 1, 3

Post-Influenza Infection Vaccination

The primary consideration is clinical recovery from acute illness, not a specific time interval after infection. 4

• Confirm resolution of fever without antipyretics and ensure acute symptoms have substantially improved before administering vaccine. 4
• High-risk individuals should be prioritized for vaccination immediately upon recovery to minimize their window of vulnerability. 4
• Do not assume that recent influenza infection provides adequate protection for the remainder of the season, as influenza activity can peak as late as March. 4

Common Pitfalls to Avoid

• Do not delay vaccination waiting for "optimal" timing - vaccination in December or later is still beneficial in most seasons. 1
• Do not withhold vaccination from children with minor illnesses - only acute febrile illness requires deferral. 1, 4
• Do not forget the second dose for young children - children aged 6 months-8 years requiring 2 doses must receive both for optimal protection. 3, 2
• Do not use live attenuated vaccine in pregnant women or immunocompromised persons - only inactivated or recombinant vaccines are appropriate. 3, 4