Influenza Vaccines
Introduction to Influenza Vaccines
Influenza vaccines are crucial public health tools designed to prevent and mitigate the impact of seasonal and pandemic influenza. These vaccines have been in use for decades and continue to evolve to meet the challenges posed by the ever-changing influenza viruses.
Key points:
- First influenza vaccine developed in the 1940s
- Annual reformulation to match circulating strains
- Essential component of global influenza prevention strategies
- Recommended for widespread use, especially in high-risk populations
- Ongoing research focuses on developing universal influenza vaccines
Influenza Virus and Disease
Influenza Viruses
- RNA viruses of the Orthomyxoviridae family
- Four types: A, B, C, and D (A and B cause seasonal epidemics)
- Subtypes of Influenza A based on surface proteins (hemagglutinin and neuraminidase)
- Undergo frequent antigenic drift and occasional antigenic shift
Influenza Disease
- Acute respiratory illness characterized by fever, cough, myalgia, and fatigue
- Incubation period: 1-4 days
- Can lead to severe complications, especially in high-risk groups
- Annual global burden: 3-5 million severe cases and 290,000-650,000 deaths
Transmission
Primarily spread through respiratory droplets and contact with contaminated surfaces. Highly contagious, especially in closed settings.
Types of Influenza Vaccines
Several types of influenza vaccines are currently available:
1. Inactivated Influenza Vaccines (IIV)
- Most common type
- Contain inactivated virus particles
- Administered intramuscularly
- Subtypes: Trivalent (IIV3) and Quadrivalent (IIV4)
2. Live Attenuated Influenza Vaccine (LAIV)
- Contains weakened live viruses
- Administered intranasally
- Quadrivalent formulation
- Approved for use in certain age groups
3. Recombinant Influenza Vaccine (RIV)
- Produced using recombinant DNA technology
- Does not require egg-based production
- Quadrivalent formulation (RIV4)
4. Cell-Culture-Based Vaccines
- Produced using cell culture rather than eggs
- Potential for faster production
- Quadrivalent formulation
5. Adjuvanted Vaccines
- Contain an adjuvant to enhance immune response
- Particularly useful in older adults
- Example: MF59-adjuvanted vaccine
Influenza Vaccine Development
Strain Selection Process
- WHO Global Influenza Surveillance and Response System (GISRS) monitors circulating strains
- Biannual WHO consultations for strain recommendations (February for Northern Hemisphere, September for Southern Hemisphere)
- Strains selected based on antigenic and genetic analyses, epidemiological data, and vaccine efficacy studies
Production Methods
- Egg-based production: Traditional method, takes about 6 months
- Cell-based production: Faster, not dependent on egg supply
- Recombinant technology: Rapid production, highly scalable
Composition
Typically includes:
- Two Influenza A strains (H1N1 and H3N2)
- One or two Influenza B strains (Victoria and/or Yamagata lineages)
Efficacy and Safety of Influenza Vaccines
Efficacy
- Varies annually depending on match between vaccine and circulating strains
- Typical efficacy: 40-60% when well-matched
- Can reduce severity of illness even when not fully protective
- Effectiveness may be lower in certain populations (e.g., older adults)
Safety Profile
- Generally well-tolerated
- Common side effects: Injection site reactions, mild systemic symptoms
- Rare adverse events: Guillain-Barré syndrome (1-2 cases per million vaccinations)
- LAIV: Contraindicated in certain groups due to theoretical risks
Duration of Protection
Protection typically lasts through one influenza season but can wane over time, especially in older adults. Annual vaccination is recommended due to antigenic drift and waning immunity.
Influenza Vaccination Schedule
Timing
- Annual vaccination recommended
- Optimal timing: Early fall, before influenza activity begins
- Can be given throughout influenza season
Dosing
- Adults and children ≥9 years: Single dose annually
- Children 6 months to 8 years:
- Two doses (separated by at least 4 weeks) if first time receiving influenza vaccine or if vaccination history is unknown
- Single dose if previously received ≥2 doses of influenza vaccine
Route of Administration
- IIV and RIV: Intramuscular injection
- LAIV: Intranasal spray
Influenza Vaccination in Special Populations
Pregnant Women
- Recommended at any stage of pregnancy
- IIV preferred; LAIV contraindicated
- Provides protection to both mother and infant
Older Adults (≥65 years)
- High-dose or adjuvanted vaccines may be preferable
- Important due to increased risk of complications
Immunocompromised Individuals
- IIV or RIV recommended; LAIV contraindicated
- May have reduced vaccine response
Healthcare Workers
- Annual vaccination strongly recommended
- Important for protecting both workers and patients
Children
- Recommended for all children ≥6 months
- LAIV an option for healthy children ≥2 years in some countries
Challenges and Considerations in Influenza Vaccination
Antigenic Drift and Shift
- Constant viral evolution necessitates annual vaccine updates
- Potential for pandemic strains through antigenic shift
Vaccine Hesitancy
- Misconceptions about vaccine safety and efficacy
- Need for effective public health communication
Production Challenges
- Time constraints in egg-based production
- Potential for mutations during egg adaptation
Variable Effectiveness
- Efficacy depends on match with circulating strains
- Reduced effectiveness in certain populations
Global Access and Equity
- Disparities in vaccine availability and distribution
- Need for improved global vaccination strategies
Future Directions in Influenza Vaccination
Universal Influenza Vaccine
- Targeting conserved viral proteins
- Potential for broader, longer-lasting protection
- Multiple candidates in clinical trials
Improved Production Methods
- Advancing cell-based and recombinant technologies
- Exploring mRNA vaccine platforms
Enhanced Delivery Systems
- Microneedle patches for painless administration
- Oral and sublingual vaccine formulations
Personalized Vaccination Approaches
- Tailoring vaccines based on individual immune responses
- Optimizing vaccination strategies for specific populations
Improved Surveillance and Prediction
- Enhancing global surveillance networks
- Utilizing big data and AI for strain prediction
Influenza Vaccines
- Q: What types of influenza viruses do seasonal flu vaccines typically protect against? A: Influenza A (H1N1 and H3N2) and Influenza B
- Q: How often are influenza vaccine compositions updated? A: Annually
- Q: What is the most common method of administering influenza vaccines? A: Intramuscular injection
- Q: What is the minimum age for receiving most influenza vaccines? A: 6 months
- Q: How many doses of influenza vaccine are recommended for children 6 months to 8 years receiving it for the first time? A: 2 doses
- Q: What is the interval between doses for children requiring two doses of influenza vaccine? A: At least 4 weeks
- Q: What is the name of the intranasal influenza vaccine? A: FluMist (LAIV)
- Q: What type of influenza vaccine is FluMist? A: Live attenuated influenza vaccine (LAIV)
- Q: What is the age range for which FluMist is approved in the US? A: 2-49 years old
- Q: What is the typical effectiveness of seasonal influenza vaccines? A: 40-60%
- Q: In which month does influenza vaccination typically begin in the Northern Hemisphere? A: September or October
- Q: What is the name of the high-dose influenza vaccine designed for older adults? A: Fluzone High-Dose
- Q: How many influenza virus strains does a quadrivalent vaccine contain? A: 4 strains
- Q: What is the main advantage of cell-based influenza vaccines over egg-based vaccines? A: Faster production and avoidance of egg-adapted changes
- Q: What is the name of the first approved recombinant influenza vaccine? A: FluBlok
- Q: What protein is produced using recombinant DNA technology in FluBlok? A: Hemagglutinin (HA)
- Q: What is the typical dosage of standard-dose influenza vaccines for individuals 3 years and older? A: 0.5 mL
- Q: What is the reduced dosage of some influenza vaccines for children 6-35 months old? A: 0.25 mL
- Q: What is the storage temperature requirement for most influenza vaccines? A: 2-8°C (35-46°F)
- Q: How long does it typically take for immunity to develop after influenza vaccination? A: About 2 weeks
- Q: What is the name of the adjuvanted influenza vaccine designed for older adults? A: Fluad
- Q: What is the adjuvant used in Fluad? A: MF59
- Q: In which year was the first influenza vaccine licensed for use in the United States? A: 1945
- Q: What percentage of the global population is estimated to be affected by seasonal influenza annually? A: 5-10%
- Q: What is the estimated number of deaths caused by seasonal influenza globally each year? A: 290,000 to 650,000
- Q: What is the main surface glycoprotein targeted by most influenza vaccines? A: Hemagglutinin (HA)
- Q: What is antigenic drift in the context of influenza viruses? A: Small, gradual changes in the virus genes
- Q: What is antigenic shift in the context of influenza viruses? A: Abrupt, major change in influenza A viruses
- Q: Which influenza virus type is capable of causing pandemics? A: Influenza A
- Q: What is the name of the global surveillance network that monitors influenza virus evolution? A: Global Influenza Surveillance and Response System (GISRS)
Disclaimer
The notes provided on Pediatime are generated from online resources and AI sources and have been carefully checked for accuracy. However, these notes are not intended to replace standard textbooks. They are designed to serve as a quick review and revision tool for medical students and professionals, and to aid in theory exam preparation. For comprehensive learning, please refer to recommended textbooks and guidelines.
