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The estimated effectiveness of the influenza vaccine is 21% in preventing influenza transmission among family members
Last reviewed: 03.07.2025
A new study by researchers at Vanderbilt University found that the risk of influenza infection among household members is 18.8%, and the effectiveness of vaccines against secondary infections is estimated at 21%. The work, published in JAMA Network Open, is based on data from 700 people infected with the flu and their 1,581 household members.
Research Methodology
The study spanned three respiratory seasons (2017–2020) in Tennessee and Wisconsin. Participants presented to clinics with flu-like symptoms. Scientists analyzed nasal swabs and kept symptom diaries for seven days.
- The average age of those infected is 13 years.
- Half of the participants (49.1%) were vaccinated.
- The average age of household members was 31 years, of whom 50.1% received the vaccine, 22.5% fell ill with influenza during the observation period.
Key Results
Risk of transmission:
- The risk of infection among household members was 18.8%.
- The highest risk was observed among children under five years of age: 20.3% for strain A and 15.9% for strain B.
- 7% of secondary infections were asymptomatic.
Vaccine Efficacy (VE):
- The overall efficacy against secondary infections was 21%.
- VE vs. B strain:
- 56.4% overall.
- 88.4% for children 5–17 years old.
- 70.8% for adults 18–49.
- VE against strain A was only 5% (for subtypes H1N1 - 21.4%, for H3N2 - −26.9%).
Conclusions
The study confirmed the high risk of influenza transmission in households, especially for young children. Vaccines, although less effective against the A strain, still reduced the likelihood of infection, especially with the B strain.
To reduce the spread of infection in families, additional measures are recommended:
- Isolation of the sick.
- Improving ventilation.
- Maintaining hand hygiene.
- Disinfection of surfaces.
- Use of masks.
- Preventive use of antiviral drugs.
These measures, combined with vaccination, will help reduce the incidence of the disease and improve protection for the most vulnerable groups of the population.