The Role of Vaccination in Preventing Infectious Diseases
Vaccination is the most effective medical intervention for preventing infectious diseases, reducing morbidity, mortality, and healthcare costs across all populations by inducing long-lasting immunological memory and herd immunity. 1, 2
Core Mechanisms of Vaccine Protection
Vaccines work through two fundamental mechanisms that have proven successful over 200 years of use:
- Individual protection through induction of long-lasting immunological memory that generates neutralizing antibodies and cellular immune responses 3
- Population-level protection through herd immunity, which reduces disease transmission even among unvaccinated individuals 1, 3
The most successful vaccines target pathogens during their bacteremic or viremic phases, before they replicate in target organs, making them susceptible to neutralizing antibodies 3. Examples include poliomyelitis and infections caused by encapsulated bacteria like Streptococcus pneumoniae 3.
Evidence of Clinical Impact
Influenza Prevention
Influenza vaccination prevents 70-90% of illness in healthy adults under 65 years when vaccine strains match circulating viruses. 1
- Vaccination reduces work absenteeism and healthcare resource utilization in healthy adults 1
- In older adults (≥65 years), influenza causes 30-150 deaths per 100,000 persons during epidemics, with >90% of pneumonia and influenza deaths occurring in this age group 1
- More than 40,000 influenza-associated deaths occurred during six of eleven U.S. epidemics between 1972-1995 1
- High-dose or adjuvanted vaccines are recommended for adults ≥65 years due to superior immunogenicity in this population 4
Pneumococcal Disease Prevention
The 23-valent pneumococcal polysaccharide vaccine covers 85-90% of serotypes causing invasive pneumococcal infections in the U.S. 1
- While efficacy against non-bacteremic pneumonia remains debated, the vaccine effectively reduces life-threatening bacteremic disease 1
- Approximately 50% protective against pneumonia overall 5
Disease-Specific Outcomes
Vaccination has demonstrated clear mortality and morbidity benefits in high-risk populations:
- Diabetes patients: Influenza vaccination reduces hospital admissions during epidemics and lowers cardiovascular mortality in those with cardiovascular disease 1, 4
- Cancer patients: Infections are a significant cause of morbidity and mortality, making vaccination a critical preventive measure despite potential immunocompromise 1
- HIV-infected persons: Pneumococcal vaccination shows no adverse effect on patient survival, contrary to theoretical concerns about immune stimulation 1
Special Populations Requiring Tailored Approaches
Immunocompromised Patients
Live-attenuated vaccines are contraindicated during active immunosuppression, but inactivated vaccines remain safe and should be administered. 1, 6
For patients with hematological malignancies:
- Live-attenuated varicella vaccine must be avoided during treatment and for 24 months after completing immunosuppressive therapy 6
- Inactivated vaccines (influenza, pneumococcal, tetanus) can be given safely, though antibody responses may be reduced 1
- Household contacts should receive all recommended vaccines to create a protective barrier 6
Patients with Autoimmune Disease
Inactivated vaccines do not increase disease activity in systemic lupus erythematosus (SLE) and should be administered per standard guidelines. 1, 7
- Tetanus toxoid achieves protective antibody response in ~90% of SLE patients, similar to the general population 7
- Most immunosuppressive medications do not interfere with tetanus toxoid antibody development 7
- Exception: If rituximab was given within 24 weeks and urgent tetanus protection is needed, use passive immunization with tetanus immunoglobulin 7
Older Adults (≥65 years)
Age-related immune changes reduce vaccine efficacy, necessitating enhanced formulations:
- Standard influenza vaccines show only 30-50% efficacy in older adults 5
- Higher antigen doses, adjuvants (MF59), and intradermal administration improve immunogenicity 5
- High-dose quadrivalent inactivated influenza vaccine is specifically recommended for this age group 4
- Recombinant herpes zoster vaccine with AS01B adjuvant demonstrates ~90% efficacy even in the oldest age groups, compared to 51% for the older live-attenuated vaccine 5
Critical Implementation Strategies
Timing Considerations
Administer vaccines during routine healthcare visits or hospitalizations before the disease season to maximize coverage. 1
- Influenza vaccination should begin each September 1
- For immunocompromised patients requiring urgent treatment, complete vaccination at least 4 weeks before starting immunosuppressive therapy when possible 6
- Yearly influenza vaccination is required because immunity declines within one year 1
Overcoming Coverage Gaps
Despite proven efficacy, vaccination coverage remains suboptimal:
- Adult vaccination coverage is well below Healthy People 2020 targets for most vaccines 8
- Racial/ethnic disparities persist and are widening for some vaccines 8
- Standing orders and systematic intervention strategies significantly increase coverage 1, 9
- Vaccinating healthcare workers reduces mortality among their patients 9
Common Pitfalls and How to Avoid Them
Do not withhold inactivated vaccines from immunocompromised patients due to concerns about efficacy—partial protection is better than no protection. 1
- Even with reduced antibody responses, immunocompromised patients derive clinical benefit from vaccination 1
- The most common error is assuming vaccines are contraindicated in immunosuppression; only live-attenuated vaccines are contraindicated 6
Do not assume egg allergy is an absolute contraindication to influenza vaccine. 1
- Only anaphylactic hypersensitivity to eggs contraindicates influenza vaccination 1
- Mild egg allergy does not preclude vaccination 1
Do not delay vaccination waiting for "optimal" formulations when standard vaccines are available. 4
- Any influenza vaccine is preferred over no vaccine, and vaccination "today" is preferred over delay 4
- If high-dose or adjuvanted vaccine is unavailable, administer standard-dose vaccine 4
Safety Profile
Vaccines have an excellent safety record, with most adverse events being minor:
- Most common side effect is mild soreness at injection site 1
- Influenza vaccine contains only noninfectious viruses and cannot cause influenza 1, 4
- Guillain-Barré syndrome within 6 weeks of previous influenza vaccination is a contraindication to revaccination 1, 4
Post-marketing surveillance remains critical for detecting rare adverse events not identified in clinical trials, as demonstrated by the withdrawal of Rotashield (intussusception) and LYMErix (autoimmune arthritis) 1. However, these isolated events should not undermine confidence in the overall safety and necessity of vaccination programs 1.
Economic and Public Health Impact
Vaccination is the most cost-effective healthcare intervention, preventing substantial morbidity, mortality, and healthcare expenditures. 1, 2