Vaccination%20for%20control%20of%20H5N1%20avian%20influenza%20in%20Viet%20Nam

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Vaccination for control of H5N1 avian influenza
in Viet Nam

• Dung Do
• Department of Animal Health, MARD, Viet Nam
• dung.dah_at_gmail.com

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Introduction

• By mid-2005 Viet Nam had experienced the most
  human cases of disease associated with H5N1 HPAI
  (93 cases 42 fatal by December 2005)
• Viet Nam has over 230 million poultry with about
  7 to 8 million households involved in rearing
  poultry
• Large population of ducks (c. 50 - 60 million)

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Measures implemented in 2005

• In the second half of 2005 a number of measures
  were implemented or strengthened to reduce the
  risk of infection with H5N1 viruses
• Vaccination was initially implemented in all
  provinces covering most high risk populations of
  poultry
• Vaccination included village households where
  most of the human cases had occurred
• Other measures included bans on duck breeding
  (not strictly enforced), public awareness
  campaigns and closure of urban markets all
  leading to a reduced demand for poultry by
  consumers

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AI in Viet Nam post-vaccination

• No reported cases of disease in humans for over
  one year since vaccination was fully implemented
• No reports of disease in fully vaccinated poultry
• The effects of vaccination difficult to separate
  from that of other measures
• However, vaccination would have reduced the
  susceptibility of a significant part of the
  poultry population

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Vaccination how performed

• Strong central direction (from PM down)
• Strong support at commune level
• Free for smallholders
• Large commercial farms purchased own vaccine and
  applied at recommended age

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Vaccination
Vaccination point
door to door
large commercial farms
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Quantity of vaccine doses imported
Periods Types of vaccine Imported (million doses)
Phase I (2005-2006) H5N1 H5N2 365 275
Phase II (2007-2008) H5N1 H5N9 250 9
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Post-vaccination surveillance

• Demonstrated that Chinese vaccines used are
  capable of producing acceptable levels of
  immunity one month post-vaccination based on
  empirical criteria
• gt70 of flock has antibody log24
• flock GMT gt20
• Virus sequencing work minor changes (Clade 1 and
  2.3 present), not affect immunity

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Temporal Pattern of HPAI outbreaks in Vietnam
Temporal Pattern of 2003/4 (1st), 2004/5 (2nd),
late 2005 (3rd) and 2006/7 (4th) AI Epidemics
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No. of outbreaks by month, 2007
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Issues
Vaccination has proven to be challenging

• Logistics vaccines, cold chains, etc.
• Vaccinator training
• Payment of vaccinators
• Sustainability
• Cost (and benefits) about 2c/dose
• Lab and field capacity to do surveillance

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Future strategy

• Vaccination continues to play a key role in AI
  controlling in Viet Nam
• Vaccination seen as a component of an integrated
  approach, but not a separate one
• Vaccination strategy to modify
• A single mass campaign a year (instead of twice a
  year as present)
• Farmers will have to share some costs of regular
  vaccination
• Enhance field surveillance