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• Eight segmented pieces of RNA, a structure that permits the introduction of new RNA. This is called genetic reassortment. This is called antigenic shift.
• The hemagglutinin spikes which provide viral attachment to cell membranes. They are strain specific antigens that mutate frequently because of inefficient proofreading by RNA polymerase. This is called antigenic drift.
• And ditto for the Neuraminidase spike, which provides release from cell membranes
FAQ’s
• Type A: The Main Player– It causes annual outbreaks– It mutates easily. This is called antigenic drift and
is why the vaccine changes every year, usually causing an epidemic affecting 10% to 20% of the population.
– It is susceptible to RNA reassortment, where a portion of avian influenza RNA is inserted. This is called antigenic shift and is responsible for pandemics or infections occurring over a wide geographic area and affecting a high proportion of the population.
– It is characterized by the H and N antigens.
Five Pandemics
• 1918: Possibly an avian influenza strain that adapted to infect humans.
• 1957 and 1968: A human/avian reassortment strain.
• 2009: A human/swine/avian reassortment virus.
Transmission
• Person to Person
• Viral shedding—day prior to symptom onset—5-7 days after symptom onset
• Can get from pigs not from eating pork
Vaccination
• EVERYONE >6months and older• IM (inactivated) Intranasal (live attenuated)• Intranasal NOT USED IN: chronic disease,
immunsuppression, pregnancy, prior h/o GB from prior vaccinations
• SMALL AMOUNTS of EGG in each• Anaphylaxis is rare• What do we carry? • Efficacy: 50%-80% rate of protection if closely
matched
Vaccine
Three strains: (always A-A-B) this year:
-A-California h1n1-”like” virus
-A-Perth h3n2 ”like” virus
-B Brisbane
Every year the strains are selected based on worldwide surveillance for most active strains– a little guess-work involved
Treatment & PPX
• Oseltamivir: TAMIFLU• Zanamavir: Ralenza• Rx for Type A &B• Low levels of resistance• In 48 hours TREAT (as per Dr. Chung)• PPX: NH Residents within 48 h, Case by
caseBabies, pregnant women