What is the recommended treatment and prevention for influenza (flu) with the influenza vaccine (flu vaccine)?

Influenza Prevention and Treatment with Vaccination

Annual influenza vaccination is strongly recommended for all persons ≥6 months of age who do not have contraindications, and this remains the cornerstone of influenza prevention regardless of prior vaccination history. 1

Who Should Receive the Influenza Vaccine

Universal annual vaccination is indicated for:

• All children ≥6 months of age, including healthy children and those with chronic medical conditions 2
• All adults, with special emphasis on persons ≥65 years of age 2
• Pregnant women at any stage of pregnancy 2
• Residents of nursing homes and chronic-care facilities 2
• Healthcare workers and household contacts of high-risk individuals 2
• Persons with chronic medical conditions (cardiovascular disease, pulmonary disease, diabetes, immunosuppression) 2

Vaccine Selection and Administration

For the 2023-24 season and beyond, inactivated influenza vaccine (IIV) is the primary recommended formulation:

• Quadrivalent formulations (IIV4) are preferred and contain protection against four influenza strains (two influenza A subtypes and two influenza B lineages) 1
• Live attenuated influenza vaccine (LAIV) should only be used when a patient refuses IIV and is appropriate by age (≥2 years) and health status 2
• The 2016-2017 season data showed poor effectiveness of LAIV4, particularly against influenza A(H1N1)pdm09, leading to the recommendation against its routine use 2

For adults ≥65 years, preferentially use one of these enhanced formulations:

• High-dose quadrivalent inactivated vaccine (HD-IIV4) at 0.7 mL per dose 1
• Quadrivalent recombinant vaccine (RIV4) at 0.5 mL per dose 1
• Quadrivalent adjuvanted inactivated vaccine (aIIV4) at 0.5 mL per dose 1

Dosing Schedule

Children 6 months through 8 years require special attention:

• Children receiving influenza vaccine for the first time need 2 doses separated by at least 4 weeks 2, 1
• Children who received only 1 dose in their first season of vaccination should receive 2 doses in the subsequent season 2
• After completing the initial 2-dose series, only 1 dose annually is needed thereafter 2

All other age groups require only 1 dose annually 2, 1

Optimal Timing

Vaccination timing should follow this algorithm:

• For most persons needing only 1 dose: vaccinate during September or October 1
• For children 6 months-8 years requiring 2 doses: begin as soon as vaccine is available, including July-August, to ensure completion before influenza season peaks 1
• For adults ≥65 years and pregnant women in first/second trimester: avoid July-August vaccination unless later vaccination may not be possible 1
• Continue offering vaccine throughout the influenza season, even after community influenza activity is documented 2

Critical caveat: Antibody levels can decline within months after vaccination, which is why vaccination before October should generally be avoided in nursing homes 2. However, the need for annual revaccination is absolute because immunity wanes significantly within one year 2, 3.

Route of Administration

Intramuscular injection is the standard route:

• Adults and older children: deltoid muscle 2, 1
• Infants and young children: anterolateral thigh 2, 1
• Use needle length >1 inch for adults and older children 2

Egg Allergy Considerations

All children and adults with egg allergy of any severity can receive influenza vaccine without additional precautions beyond routine vaccination procedures. 2 This represents a significant evolution from earlier guidelines that required physician consultation for severe egg allergy 2.

Vaccine Effectiveness

Recent effectiveness data demonstrates variable but meaningful protection:

• 2023-24 season: VE against outpatient visits was 59-67% in children and 33-49% in adults; VE against hospitalization was 52-61% in children and 41-44% in adults 4
• 2021-22 season showed reduced effectiveness (16%, not statistically significant) against the predominant A(H3N2) strain, highlighting year-to-year variability 5
• Even when vaccine match is suboptimal, vaccination remains effective at preventing severe outcomes including hospitalization and death 2

The vaccine cannot cause influenza because it contains only noninfectious, inactivated viruses 3. This is a critical point for patient education, as coincidental respiratory illness occurring after vaccination is unrelated to the vaccine itself 2.

Side Effects

Common and expected reactions include:

• Local soreness at injection site (10-64% of recipients) lasting up to 2 days 2, 3
• Fever occurs in 10-35% of children <2 years but rarely in older children and adults 2
• Systemic symptoms (malaise, myalgia, headache) are uncommon and typically affect only those without prior influenza antigen exposure 2, 3

Serious adverse events are extremely rare:

• Guillain-Barré Syndrome risk is estimated at most 1-2 cases per 1 million vaccinees 6
• Immediate allergic reactions (hives, angioedema, anaphylaxis) occur rarely 2

Antiviral Medications as Adjunct

Antiviral medications complement but do not replace vaccination:

• Neuraminidase inhibitors (oseltamivir, zanamivir) are recommended for treatment and chemoprophylaxis 2
• Amantadine and rimantadine should not be prescribed due to widespread resistance 2
• Antivirals are especially important when vaccine effectiveness is reduced 5
• Treatment should be initiated as soon as possible, preferably within 24 hours of symptom onset 7

Repeated Annual Vaccination

Annual vaccination is necessary and beneficial regardless of prior vaccination history:

• Repeated vaccination (including current season) is consistently more effective than no current vaccination 8
• There is no evidence of negative interference from repeated annual vaccination 8
• Vaccine composition changes annually based on predicted circulating strains 2, 3

Common Pitfalls to Avoid

• Do not delay vaccination waiting for "peak season" - early vaccination is better than missed vaccination 2
• Do not withhold vaccine from egg-allergic patients - this outdated practice denies protection 2
• Do not use previous season's vaccine - antigenic composition changes annually 2
• Do not forget the second dose in young children receiving vaccine for the first time - single-dose series provides inadequate protection 2, 1
• Do not assume vaccine failure means vaccination is futile - even with suboptimal match, vaccine prevents severe outcomes and death 2