Influenza Virus and Vaccines Study Guide

Type: Negative sense RNA genome
Classification: Family Orthomyxoviridae
Genera & Species: - Alphainfluenzavirus (Influenza A virus) - Betainfluenzavirus (Influenza B virus) - Gammainfluenzavirus (Influenza C virus) - Deltainfluenzavirus (Influenza D virus) - Note: Distinct strains affect mammals but some variants infect fish and amphibians.

Influenza A Virus: - Total subtypes based on surface antigens: 18 HA (H1–H18), 11 NA (N1–N11) - Currently circulating in humans: A(H1N1)pdm09 (pandemic strain), A(H3N2) - Key Point: Only Influenza A causes pandemics.
Influenza B Virus: - Classification based on lineages: B/Yamagata and B/Victoria - Higher morbidity and mortality in children, constituting about 23% of global cases.
Influenza C Virus: Less frequently detected, causes milder diseases.
Influenza D Virus: Primarily affects cattle; no known infections in humans.

Annual Impact: Influenza B associated with an estimate of 23% of influenza cases globally. - Contributes approximately 7.9 million lower respiratory infections and 1.4 million hospital admissions each year. - Highest burden seen in school-aged children (0-18 years), with 52% of pediatric deaths attributed to Influenza B.
Economic Cost: US$3.5 billion annually in healthcare surcharges; 37% attributed to Influenza B.
Eradication Viability: - No animal reservoir for the Influenza B virus, making eradication conceivably easier than Influenza A. - Lack of evidence for significant animal reservoirs creates a pathway for potential eradication strategies.

Transmission Routes: - Droplets: >10 μm; primarily affect upper respiratory tract. - Aerosols: <5 μm; reach lower respiratory tract. - Direct Contact: Transmitted via mucus membranes through both direct interaction and contaminated objects.
Contributing Factors: - Environmental conditions (humidity, temperature), vaccination status, age, social interactions affect viral transmission.

Typical symptoms include: - Sudden onset of fever - Dry cough (may persist >2 weeks) - Headaches - Muscle/joint pain - Severe malaise - Sore throat - Runny nose
Most individuals recover within a week, but severity varies.

Age Risk Groups: - Adults aged 65+ - Children under 2 years - Pregnant individuals
Associated Health Issues: - Chronic lung diseases, heart diseases, blood disorders such as sickle cell disease, metabolic disorders, immune system disorders, neurological conditions.

Direct Pathology: Viral replication leads to lung inflammation and epithelial cell death (both apoptosis and necrosis).
Immune Response: Both innate (cytokine production, immune cell recruitment) and adaptive responses causing exacerbated inflammation and potential tissue damage.
Key Complications: Acute pneumonia in 30-40% of hospitalized cases, predominantly from Influenza A.

Antigenic Drift: Gradual mutations in the virus leading to variability.
Antigenic Shift: Reassortment of genome segments leading to new strain formation, which may cause pandemics.

Existing Treatments: - Neuraminidase inhibitors (NAIs): Oseltamivir, Zanamivir - M2 ion channel inhibitors: Amantadine, Rimantadine
Research: Ongoing studies target drug resistance and bioavailability improvements.

Complexity due to rapid mutations and variability among strains. - H and N proteins involved in cell entry and infection: 18 H types and 11 N types.
Vaccine Development Timeline: Vaccines produced approximately 6 months prior to flu season; effectiveness varies annually (historically around 52% - 70%).

Current vaccines used based on age groups and clinical risk: - For ages 6 months to <2 years: IIVC or LAIV - Ages 2-18 in clinical risk: IIVC or LAIV - Adults 18-64 in clinical risk: IIVC or IIVr - Ages 65 and older: IIV-HD or adjuvanted vaccines.

Vaccines under development targeting multiple strains simultaneously (multivalent nucleoside-modified mRNA vaccines) may provide broader protection.
Importance of continued research and public health measures to improve vaccine effectiveness and reduce flu burden annually.