How do I prevent influenza?

How to Prevent Influenza

Annual influenza vaccination is the single most effective method for preventing influenza infection and its complications, and should be administered to all persons aged 6 months and older starting as soon as vaccine becomes available each fall. 1, 2

Primary Prevention: Annual Vaccination

Who Should Be Vaccinated

Universal vaccination is now recommended for all persons 6 months of age and older, representing a shift from earlier risk-based strategies to comprehensive population protection. 1, 3

Priority groups requiring vaccination include:

• All persons ≥65 years of age - this group accounts for 80-90% of influenza-related deaths and experiences 2- to 5-fold increases in hospitalization rates during epidemics 1, 2
• All persons aged 50-64 years - 24-32% have chronic medical conditions placing them at high risk, yet only 40-41% receive vaccination 1
• All children 6 months through 18 years of age - children under 5 years, especially infants under 1 year, have hospitalization rates of 100-500 per 100,000 population, comparable to elderly adults 1, 3
• Pregnant women at any stage of pregnancy - third-trimester hospital admissions during influenza season are five times higher than pre-pregnancy rates 1
• Persons of any age with chronic pulmonary, cardiovascular, renal, or metabolic diseases - these individuals have influenza-related hospitalization rates of 56-635 per 100,000 compared to 13-60 per 100,000 in healthy persons 1
• Residents of nursing homes and chronic-care facilities 1, 2
• All healthcare workers - to protect themselves and prevent transmission to high-risk patients 1
• Household contacts and caregivers of high-risk persons, including caregivers of infants under 6 months who cannot receive vaccine themselves 1, 3

Vaccine Dosing Schedules

For children 6 months through 8 years receiving influenza vaccine for the first time:

• Administer 2 doses separated by at least 4 weeks 1, 4, 3
• Both doses should ideally be given before the end of October to ensure protection before peak influenza activity 4
• If a child received only 1 dose in their first year of vaccination, they require 2 doses the following season 1

For children 6-35 months:

• Dose is either 0.25 mL or 0.5 mL depending on the specific vaccine product 4
• Fluzone: either 0.25 mL or 0.5 mL 4
• Afluria: 0.25 mL 4
• Fluarix, FluLaval, Flucelvax: 0.5 mL 4

For children ≥36 months and adults:

• Single 0.5 mL dose annually 4, 3
• Previously vaccinated children need only 1 dose per year 1, 3

Optimal Timing

Begin vaccination in October and continue through November, though vaccination should continue throughout the entire influenza season as long as vaccine is available. 1, 2

• Influenza activity often extends through February, March, or later 2
• Do not delay vaccination waiting for "perfect" timing - vaccine effectiveness remains substantial for 5-6 months despite some waning immunity 2
• Continue offering vaccination even after community influenza activity has been documented 1

Vaccine Effectiveness

When vaccine and circulating strains are well-matched, vaccination achieves:

• 70-90% effectiveness against influenza illness in healthy adults under 65 years 2
• 80% reduction in deaths among elderly nursing home residents, even when effectiveness against illness itself is only 30-40% 2
• 50-60% reduction in hospitalization or pneumonia in high-risk institutionalized elderly 2
• 42-47% reduction in all-cause mortality among community-dwelling elderly 2
• 53-86% efficacy against influenza-related hospitalizations in children 3
• 30% reduction in influenza-associated otitis media in children 2

Common Vaccination Pitfalls to Avoid

• Minor illnesses with or without fever do NOT contraindicate vaccination - only defer during acute febrile illness until symptoms resolve 2
• Do not fail to complete the two-dose series in vaccine-naive children under 9 years - a single dose provides inadequate protection 3
• Administer vaccine during routine healthcare visits or hospitalizations before influenza season to maximize coverage rates rather than requiring special visits 1, 2
• Recent viral infections without fever are NOT contraindications 2

Adjunctive Prevention: Antiviral Chemoprophylaxis

Antiviral medications are an adjunct to vaccination, NOT a substitute, and should be reserved for specific high-risk situations to prevent resistance. 1, 2, 5

When to Use Antiviral Prophylaxis

Oseltamivir 75 mg once daily for 10 days is the preferred agent for chemoprophylaxis in the following situations: 6, 5

• Unvaccinated high-risk individuals exposed to confirmed influenza within 48 hours during a seasonal epidemic 5
• Institutional outbreaks in nursing homes or chronic-care facilities - for both treatment of ill individuals and prophylaxis for exposed residents 1, 5
• Short-term prophylaxis after late vaccination of high-risk persons when influenza A is already circulating in the community 1
• High-risk persons who received vaccine during a season when vaccine-strain mismatch limits effectiveness 5

Antiviral Agent Selection

Do NOT use amantadine or rimantadine - 92% of influenza A isolates show resistance to adamantanes in the United States. 1

Neuraminidase inhibitors remain effective:

• Oseltamivir (oral): 75 mg once daily for prophylaxis in persons ≥13 years; weight-based dosing for children ≥1 year 6, 5
• Zanamivir (inhaled): 10 mg (two inhalations) once daily for prophylaxis in persons ≥5 years 7
• Both agents are active against influenza A and B strains without clinically important resistance 1

Zanamivir should NOT be used in persons with underlying airways disease (asthma, COPD) due to risk of life-threatening bronchospasm. 7, 5

Duration of Prophylaxis

• Post-exposure prophylaxis: 7-10 days following exposure 6, 5
• Seasonal prophylaxis during community outbreaks: Up to 42 days in institutional settings 6
• Household post-exposure prophylaxis: 7 days starting within 48 hours of index case symptom onset 6

Additional Preventive Measures

Implement infection control practices during influenza season:

• Frequent handwashing - demonstrated to reduce respiratory diseases and remove detectable influenza A virus from hands 1
• Respiratory hygiene and cough etiquette 1
• Case isolation in institutional settings 5
• Use of face masks for exposed individuals 5

These nonpharmacologic interventions are reasonable, inexpensive adjuncts but should never replace vaccination as the primary prevention strategy. 1

Critical Contraindications

Absolute contraindications to inactivated influenza vaccine (IIV):

• Age <6 months 1
• History of severe allergic reaction (including anaphylaxis) to any vaccine component or previous influenza vaccine dose 1

Absolute contraindications to live attenuated influenza vaccine (LAIV):

• Age <2 years 1, 3
• Asthma, reactive airways disease, or chronic pulmonary/cardiovascular disorders 1
• Immunodeficiency or immunosuppressive therapy 1
• Children 2-4 years with history of wheezing in previous 12 months 3

History of Guillain-Barré Syndrome is a relative contraindication - avoid vaccination in these individuals. 1