Influenza

Goal of the Module: Understand clinical features of influenza, transmission methods, differences between flu and common cold, and influenza vaccine efficacy and safety.

Virus Characteristics: Caused by a single stranded RNA virus, part of the orthomyxovirus family.
Types of Influenza:
- Type A: Contains hemagglutinin (H) and neuraminidase (N) surface antigens.
  - 18 H subtypes (notable ones: H1, H2, H3) and 11 N subtypes (notable ones: N1, N2).
- Type B: Classified into two lineages: Yamagata and Victoria.
- Type C: Rarely causes illness in humans and often subclinical.

Primary Mode: Person-to-person through large respiratory droplets from coughing or sneezing.
Aerosol Transmission: Small droplets that linger in the air.
Indirect Contact: Touching contaminated surfaces and then touching face.
Infectious Duration: Virus can remain infectious on surfaces for hours.

Prevalence: 9 to 45 million symptomatic cases annually in the U.S. with approximately 37,000 deaths.
At-Risk Population: 65+ years old make up 80% of deaths; children under 5 show high hospitalization rates.

Virus Action: Attaches to and penetrates epithelial cells, causing replication and cell damage.
Incubation Period: About 2 days (1-4 days range).
Contagious Period: 5 to 10 days after symptom onset, peaking around 1-3 days post-symptom onset.
Common Symptoms: Rapid onset of cough, sore throat, fever, chills, malaise, muscle pains, runny nose, and gastrointestinal symptoms (vomiting/diarrhea can occur).
Duration of Symptoms: Fever lasts 3-4 days; fatigue can last weeks.

Onset: Flu has sudden onset, while cold symptoms appear gradually.
Systemic Symptoms: Fever, muscle aches, and chills are more prominent in flu.
Testing: Influenza tests can confirm diagnosis through the presence of antigens.

Antigenic Drift: Small mutations that lead to new virus strains causing annual epidemics.
Antigenic Shift: Abrupt changes from genetic recombination, leading to new pandemics (historical examples include 1918 Spanish Flu, 1957 Asian Flu, and 2009 H1N1).

Flu Seasons: Southern hemisphere - April to September; Northern hemisphere - October to May (75% peak activity occurs post-January).
Tropical Climates: Flu can occur year-round.

Serious Complications: Primary or secondary pneumonia, exacerbation of chronic conditions.
At-Risk Groups: Elderly, those with chronic conditions, pregnant women, and children under 2.

Hygiene Practices: Frequent handwashing, covering coughs/sneezes, isolation when symptomatic.

Vaccine Types: Egg-based and non-egg-based vaccines, all FDA approved for specific age groups.
Quadrivalent Vaccines: Contain two Type A and two Type B strains (as of Fall 2020).
ACIP Recommendations: Annual vaccination for all individuals 6 months and older, tailored for age and contraindications.

Flu Shots for Children: 6 months to 8 years - 2 doses if no prior vaccination; thereafter, 1 dose annually.
Brand Selection: Pharmacists should choose appropriate brands based on patient age and needs.
Insurance Billing: Must use correct administration and diagnosis codes.

Vaccine Effectiveness: Generally 40% to 60%, but milder symptoms if contracted post-vaccination.
Older Adults and Vaccine Types: Specific brands target older adults with greater efficacy.
Safety Profile: Injection site reactions are common; systemic reactions occur less frequently but can happen.
Contraindications: Severe allergic reaction to previous vaccine or components; precautions for Guillain-Barré syndrome.

Immunity Duration: Approximately 5-6 months; consider timing of vaccination to ensure protection during peak season (generally February).
Optimal Vaccination Period: Should avoid early vaccination (July/August); recommend by end of October.