Benefits and Risks of Annual Flu Vaccination for Healthy Adults
The annual influenza vaccine is highly recommended for healthy adults as it can prevent illness in 70-90% of recipients when the vaccine matches circulating strains well, reducing both personal morbidity and societal burden. 1
Effectiveness and Strain Matching
- The effectiveness of influenza vaccines depends primarily on the match between vaccine strains and circulating viruses, as well as the age and immune competence of the recipient 1
- When there is a good match between vaccine and circulating viruses, influenza vaccine prevents illness in approximately 70-90% of healthy adults under 65 years of age 1
- Each year's influenza vaccine contains three virus strains (typically two type A and one type B) representing influenza viruses likely to circulate in the upcoming season 1
- The World Health Organization determines which strains to include in each year's vaccine based on global surveillance data 2
- Recent data from the 2023-24 season shows vaccine effectiveness against influenza A ranging from 27% to 46% for adults across healthcare settings, and 46% to 59% for children and adolescents 3
- Vaccine effectiveness against influenza B was higher, ranging from 60% to 78% for adults across healthcare settings 3
- During seasons with drifted viruses (antigenic changes), vaccine effectiveness may be lower but still provides substantial benefit, especially against severe outcomes 4
Benefits for Healthy Adults
- Vaccination of healthy adults results in decreased work absenteeism and decreased use of healthcare resources 1
- The vaccine reduces the risk of severe illness, hospitalization, and death from influenza 1
- In a recent study during the 2019-2020 season (which had drifted viruses), vaccination reduced severe influenza-associated illness among adults by 32% 5
- Vaccination was 80% effective in preventing influenza-associated death 5
- Vaccination helps create herd immunity, protecting vulnerable populations who cannot be vaccinated or who respond poorly to vaccination 1
- Annual vaccination is necessary because immunity declines in the year following vaccination 2
Risks and Side Effects
- The influenza vaccine cannot cause influenza infection because it contains only noninfectious viruses that have been inactivated 2
- The most common side effect is soreness at the injection site lasting up to 2 days, reported by less than one-third of vaccine recipients 2
- Systemic reactions such as fever, malaise, and myalgia may occur infrequently, most often affecting persons with no prior exposure to influenza virus antigens 2
- Guillain-Barré Syndrome (GBS) was identified among approximately 1 per 100,000 recipients of the 1976 swine influenza vaccine, but the risk from seasonal influenza vaccines is estimated at most to be 1-2 cases per million vaccinees 4
- Immediate allergic reactions are rare but can occur in patients with egg hypersensitivity, as vaccines contain small amounts of egg protein 1
Special Considerations
- Persons with severe egg allergies should consult a physician before receiving influenza vaccination 2
- Influenza vaccination can be safely administered simultaneously with other vaccines, including pneumococcal vaccine, at different sites on the body 2
- The vaccine is made from highly purified, egg-grown viruses that have been rendered noninfectious through inactivation processes 2
Practical Implications
- The CDC recommends annual influenza vaccination for all persons aged ≥6 months, including healthy adults 3
- Vaccination before the influenza season each year is the most effective means of reducing the impact of influenza 1
- Even in years when vaccine effectiveness is moderate due to strain mismatches, vaccination still provides significant protection against severe outcomes including hospitalization and death 5
- For healthy adults, the benefits of annual influenza vaccination substantially outweigh the minimal risks 1