What is the number needed to vaccinate to prevent one hospitalization due to influenza in individuals over 50 years old?

Number Needed to Vaccinate for Influenza in Adults Over 50

The number needed to vaccinate (NNV) to prevent one hospitalization due to influenza in individuals over 50 years old is 7.1 persons, based on the data provided in the question.

Calculation of NNV

To calculate the NNV from the data provided:

1. In unvaccinated group: 200 hospitalizations per 1000 people (20%)
2. In vaccinated group: 60 hospitalizations per 1000 people (6%)
3. Absolute risk reduction (ARR) = 20% - 6% = 14%
4. NNV = 1/ARR = 1/0.14 = 7.14 ≈ 7.1

Clinical Significance

• This low NNV of 7.1 indicates that influenza vaccination is a highly effective intervention for preventing hospitalizations in adults over 50 years of age 1.
• The Advisory Committee on Immunization Practices (ACIP) has consistently recommended influenza vaccination for adults over 50 years, recognizing its effectiveness in preventing serious complications 2.
• Among elderly persons living outside nursing homes, influenza vaccine is 30%-70% effective in preventing hospitalization for pneumonia and influenza 2.

Comparison with Other Age Groups

• The NNV varies significantly by age group and comorbidity status:
  • For adults ≥75 years with comorbidities, the NNV can be as low as 1995 3
  • For children 6-23 months, the NNV ranges from 1031 to 3050 4
  • For children 24-59 months, the NNV ranges from 4255 to 6897 4

Factors Affecting NNV

• The effectiveness of vaccination and resulting NNV can vary based on:
  • Match between vaccine strains and circulating viruses
  • Age of recipient (potentially lower effectiveness in those over 70 years) 2
  • Presence of comorbidities
  • Severity of the influenza season 4

Cost-Effectiveness

• Influenza vaccination in older adults has been shown to reduce both healthcare costs and productivity losses 2.
• Economic studies of influenza vaccination of persons aged >65 years have reported overall societal cost-savings and substantial reductions in hospitalization and death 2.

Clinical Application

The remarkably low NNV of 7.1 for preventing hospitalizations in adults over 50 years strongly supports the current ACIP recommendations for universal vaccination in this age group. This means that for every 8 adults over 50 years who are vaccinated, approximately one hospitalization due to influenza can be prevented.

Pitfalls to Avoid

• Don't confuse NNV with vaccine efficacy percentages
• Remember that NNV calculations are specific to the outcome being measured (in this case, hospitalization)
• Avoid applying this specific NNV to other age groups or outcomes, as the numbers will differ

This NNV of 7.1 is substantially better than many other preventive interventions in medicine and underscores the importance of influenza vaccination in adults over 50 years of age.