06. Influenza

Question 1

Clinical Features

Answer 1

Contagious respiratory illness caused by influenza viruses that infect the respiratory tract

Transmitted via respiratory secretions of infected individual (Infected aerosols; Direct & indirect contact

Incubation period is 1 – 4 days

Infectious (contagious) period is 1 day prior to symptom onset to 5-7 days post symptom onset

Illness characterized by abrupt onset of respiratory & constitutional symptoms with resolution in 3-7 days

Potential complications: pneumonia, bronchitis, sinus infection & worsening of underlying illness

Laboratory testing: Screening (Rapid Influenza Diagnostics Tests) & Confirmatory (viral culture & RT PCR)

Question 2

Epidemiology (Occurrence, High Risk Populations, Reservoir, Transmission)

Answer 2

• Occurrence: World wide
  
  • North America: Annual epidemics, November - March
  • South America: Annual epidemics, May - September
  • Tropics: Year-round presence
• High Risk Populations
  
  • Children under 5 years
  • Adults 65 years and older
  • Pregnant women
  • Residents of nursing homes and long-term care facilities
  • Chronic medical conditions
• Reservoir:
  
  • Type A - Humans and animals
  • Type B - Humans and seals
• Transmission: Respiratory

Question 3

Basic Viral Characteristics

Answer 3

3 influenza types: A, B & C

RNA virus; RNA codes for 11 proteins

2 important surface proteins

Hemagglutinin (HA): Mediates attachment to respiratory track cells

Neuraminidase (NA): Mediates release of new virus from host cells; Target of antiviral drugs

HA & NA play an important role in the body’s immune response to influenza

Question 4

Influenza Type A

Answer 4

Rapidly evolving virus

Responsible for yearly epidemics & occasional pandemics

Infects both humans & animals

Divided into subtypes based on HA & NA

• H1 – H18 / N1 – N11
• Ex: influenza A (H3N2), influenza A (H5N1)

Further divided into strains

Question 5

Type B

Answer 5

Contribute to yearly epidemics but not pandemics

Infects only humans & seals

Broken down into lineages

Further divided into strains

Question 6

Antigenic Drift

Answer 6

Continuous, gradual changes in influenza virus genes coding for HA & NA (point mutations)

Small changes generate new viruses that are closely related and an immune system previously exposed to a similar virus would respond

Small changes accumulate over time, generating a virus that is not recognized by the body’s immune system

Causes seasonal epidemics and reason why influenza vaccine components are reevaluated each year

Question 7

Antigenic Shift

Answer 7

Abrupt major change that results in an influenza A virus with a new HA or new HA & NA proteins

• New subtype
• Dramatically different subtype

Produces a novel virus that human populations have had little to no protection against

Reason for the occurrence of historical pandemics

Question 8

Why is surveillance important for influenza?

Answer 8

Track seasonal epidemics, identify circulating influenza strains & monitor drift

Early detection of pandemics

Use data generated to make determination regarding composition of next season’s influenza vaccine

Question 9

multiple networks in U.S track flu and provide data on (5)

Answer 9

virologic surveillance

outptatient illness survillance

mortality surveillance

hospitalization surveillance

geographic spread of flu

Question 10

Influenza Vaccines (2 main types)

Answer 10

Inactivated Influenza Vaccine (IIV) / Route: Intramuscular

Live Attenuated Influenza Vaccine (LAIV) / Route: Intranasal

ACIP recommends influenza vaccine annually for all persons aged 6 months of age and older

ACIP: Adviosry Committee on Immunization Practices

Question 11

U.S. timeline to produce vaccines

Answer 11

1: WHO recommends composition for North hemisphere

2-3: FDA recommends for U.S; CDC provides seed virus

3-9: production, testing, packing, shipping

10: vaccination begins