Influenza and Vaccines

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Influenza and Vaccines
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History

• Influenza has been described as early as 400 B.C.
• Major epidemics and pandemics of influenza have
  occurred throughout history.
• The influenza pandemic of 1918 led to 20,0000,000
  deaths worldwide
• Many virologists think another influenza pandemic
  that could kill millions of humans is inevitable.

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Epidemiology

• Epidemics become unmanageable at alarming speeds
  because
• Short incubation period (1-4 days)
• One droplet can contain 100,000 to 1,000,000
  virus particles.
• Symptomatic people do not stay home spread.
• Lack of herd immunity
• Absenteeism from schools is the best indicator of
  the scale of an epidemic.

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Influenza Statistics

• 1957-1987 There were 20 influenza epidemics
  recorded in the U.S.
• 36,000-50,000 people have died as a direct or
  indirect consequence of an influenza infection
• Lets take a look at the statistics for previous
  year
• Update - Influenza Activity, United States
  September 28, 2008 - January 31, 2009

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Influenza Virus

• Ss RNA Virus
• Segmented (8 strands)
• Enveloped spikes proteins
• H - attachment N - escape (sialidase)

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Influenza Virus
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Influenza A Virus Particle

• Hemagglutinin (H)
• Glycoprotein which binds to cell receptors
• Main antigen against which neutralizing antibody
  is formed
• Neuraminidase (N
• Removes the sialic acid from the cell receptor
  after the virus has attached to it
• Decreases the viscosity of respiratory tract
• Helps virus spread in the respiratory tract

Figure 12.6c the influenza A virus structures
D, H, and N spikes.
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Influenza Virus

• Orthomyxovirus
• Strains A, B and C
• Strain A and Hemagluttinin and Neuraminidase
• Influenza A (H5N1) virus - bird flu
• Influenza A (H1N1, H1N2, and H3N2) - commonly
  circulating in humans

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Virus Evolution

• Have you ever gotten the flu shot one year and
  still came down with the flu?
• Why?
• Antigenic shift
• 2 strains and exchange of genes to make new
  strain
• Antigenic drift
• Mutation in one strain to make new strain
• New strains every year
• Need a new shot every year

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Antigenic Drift

• Responsible for seasonal influenza strains

Figure 12.13a Antigenic drift is the gradual
accumulation of new epitopes on the H protein
(and, to a lesser degree, the N protein).
Adapted from Annenberg Media. Emerging
Infectious Diseases. Rediscovering Biology
Molecular to Global Perspectives. Annenberg
Media, 1997. http//www.learner.org/channel/course
s/biology/textbook/infect.
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Antigenic Shift

• Responsible for Pandemic strains
• When two types of influenza infect the cell
• Reassortment of the RNA pieces can occur

Figure 12.13b Antigenic shift occurs when the
influenza A virus acquires a new H or N gene.
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Influenza (Flu)

• Etiology influenza virus
• Symptoms
• Early headache, malaise, congestion, sore
  throat, swollen lymph nodes, fatigue
• Peak Fever, severe congestion, myalgia,
  rhinitis, cough
• Adult known severe symptoms with risk factors
• Fluid accumulation in lungs which can lead to
  pneumonia and or breathlessness and wheezing
• Vomiting and weight loss
• Severe fever (above 102)
• Symptoms in children
• Febrile seizures with high fever
• Vomiting
• Ear infection
• Recovery
• 7 to 10 days for healthy individuals
• 2 to 5 weeks in those with risk factors
• Death occurs more often in those with risk factors

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Risk Factors

• Weakened immunity
• Age
• Young (under 2) and elderly (above 60) have
  ineffective immune system
• Smoking
• pulmonary defense system weak
• Uncontrolled diabetes
• Asthma
• Pregnancy
• Heart disease
• Immunosuppressant therapy
• Cancer, tissue transplants

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Vaccine

• Injection of antigen
• Whole agent
• Inactivated versus live attenuated
• Subunit
• Toxoid
• Immune response
• B cell activation and antibody production?Short
  term immunity
• Memory cell production?Long term immunity

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Influenza Vaccine

• Inactivated Whole Agent
• Mixture of a few influenza strains
• Strains chosen based on the most abundant strains
  infecting Asian populations the previous year.
• Immunity from vaccine or recovery from actual
  disease
• Herd Immunity
• 70 of the population immune (vaccine or active
  disease)
• Dramatically slows spread (ex. Small pox)
• What percentage of the population actually gets
  vaccinated?
• Who SHOULD be vaccinated?

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Vaccination
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Vaccine Efficacy

• Not always 100 effective
• Herd Immunity difficult to achieve
• Reasons why
• You are vaccinated for a specific strain and any
  new strain can still infect you
• New strains and genetic drift and shift
• If you have a weak immune system you dont always
  have a strong immune response to protect you
• So why bother?
• Who should bother?

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More Protection

• Prevent exposure
• Hand washing
• Dont really need antimicrobial soap! Any soap
  will do.
• Common Sense
• Antivirals MUST BE TAKEN EARLY
• Amantadine, Rimantadine
• Prevent uncoating
• Zanamivir (Relenza), and Oseltamivir (Tamiflu)
• Prevents neuraminidase from cleaving sialic acid
  during budding
• Causes viruses to clump at the cell surface,
  reducing viral spread
• There are NO antibiotics!