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Basics of Avian and Pandemic Influenza
Will pandemic flu strike again?
The Pandemic Clock is
ticking…we just don’t know what time it is.
Edgar Marcus
 University of Washington School of Medicine

The “Forgotten Pandemic”
 The influenza pandemic of 1918-19
killed more humans than any other
disease in a period of similar
duration in the history of the world.
Alfred W. Crosby, historian & author
Influenza pandemics in the 20th century
1918: “Spanish Flu”
1957: “Asian Flu”
50 million deaths
1-4 million
deaths
1968: “Hong Kong Flu”
1-4 million
deaths
An Influenza Ward during the 1918:
“Spanish Flu”
Avian strain of influenza virus
Virus was similar to current bird flu virus
Spread around the globe in 4-6 months
Infected between 25-30% of the world population
Killed 40-100 million world-wide
Majority of deaths in persons 18 to 40 years old
Influenza pandemics are recurring events
•
Influenza pandemic is NOT a one-off event.
•
They are regular events that occur a few times per century.
•
As long as the influenza virus continues to mutate we will continue to
have influenza pandemics.
•
We cannot be sure exactly when the next one will be, but experts agree
it will happen eventually.
•
The H5N1 Avian Influenza virus currently circulating in birds is the
No.1 candidate for causing
the next pandemic.
A Pandemic WILL occur:
the question is
“when and how severe will it
be”?
WHO Situational Assessment
as at May 2006
• Risk of Pandemic is great
• The risk will persist
• The evolution of the threat cannot be predicted
• The early warning systems are weak
• Reduction of morb/mort impeded by inadequate
medical supplies
• Preparation is the best protection
H5N1 - The Basics
– Avian influenza H5N1 virus in poultry flocks
– Aggressive infection - quickly kills whole flocks
– Can infect humans - mainly only people living/working with
poultry
– Over 200 people infected - more than half have died (mortality rate
>50%!!!!)
– Cannot yet easily spread from person to person
H5N1 has similarities to 1918-19 virus
THE DISEASE IN HUMANS
 Influenza viruses are normally highly species-specific, meaning
that viruses that infect an individual species (humans, certain species of
birds, pigs, horses, and seals), and only rarely spill over to cause
infection in other species.
 Of the hundreds of strains of avian influenza A viruses, only four
are known to have caused human infections: H5N1, H7N3, H7N7, and
H9N2. In general, human infection with these viruses has resulted in
with one
notable exception: the highly
pathogenic H5N1 virus.
mild symptoms and very little severe illness,
H5N1--great concern for human health
 First, the H5N1 virus has caused the greatest number of
human deaths.
 The virus has met all prerequisites
for the start of a pandemic save one:
an ability to spread efficiently
among humans.
H5N1 - The Basics

An Influenza Virus must have three attributes to
become a Pandemic Virus:
1) A novel (new) virus which humans have no
immunity 
2) The virus causes significant human illness and
death 
3) The virus can spread easily from person to person x

Avian Flu H5N1 has 2 out of 3 today…
H5N1 - The Basics

An Influenza Virus must have three attributes to
become a Pandemic Virus:
1) A novel (new) virus which humans have no
immunity 
2) The virus causes significant human illness and
death 
3) The virus can spread easily from person to
person x

Avian Flu H5N1 has 2 out of 3 today…
禽流感在公共衛生的重要性
在20世紀時的三次重大「世界性大流行」均與其病毒來自「禽
類」有關。若張三感染了「『禽』流感病毒（紅色基因）」而
他的親友李四卻感染「『人』流感病毒（藍色基因）」，那重
新洗牌八段藍色基因與八段紅色基因，容易產生一種『新』型
病毒是原來人的抗體無法抵擋的，卻又可在人群中傳播。
禽流感病毒
人流感病毒
×
新型流感病
Genetic drift
• A change that occurs on the
molecular level to effect a
change in the antigenic
properties of a bacteria or
virus.
• Antigenic drift occurs
naturally and more rapidly
in certain viruses (for
example HIV).
• It is antigenic drift which
complicates the development
of an effective HIV (AIDS)
vaccine.
As the human influenza strains are continually evolving
via these mutations, the virus is able to escape from
the human immune response and cause epidemics.
For this reason, manufacturers must change the composition
of the influenza vaccine on an annual basis in order to
ensure an accurate match is achieved with the circulating
viral strains
Genetic shift
• Antigenic shift is the
process by which different
strains of a virus, (or
different viruses), combine
to form a new subtype
• having a mixture of the
surface antigens of the
two original strains.
What is the difference between Antigenic
shift and antigenic drift?
Antigenic drift is the natural mutation over
time of known strains of influenza (or other
things, in a more general sense) which may
lead to a loss of immunity, or in vaccine
mismatch. Antigenic drift occurs in all types of
influenza including influenza A, B and C.
Antigenic shift, however, occurs only in
influenza A because it infects more than just
humans. Affected species include other
mammals and birds, giving influenza A the
opportunity for a major reorganization of
surface antigens
Antigenic shift vs antigenic drift:
Antigenic drift is the natural
mutation over time of known strains of
influenza (or other things, in a more general
sense) which may lead to a loss of immunity,
or in vaccine mismatch. Antigenic drift occurs
in all types of influenza including influenza A,
B and C.
Antigenic shift, however, occurs
only in influenza A because it infects more
than just humans. Affected species include
other mammals and birds, giving influenza A
the opportunity for a major
reorganization of surface
antigens.
How is Influenza Spread?
 Infectivity period: 1 day before, 14 days after
 1. Contact transmission:

Direct - Kissing

Indirect – Sharing
 2. Mainly by “droplet” spread:

Coughing, sneezing and talking

Mucous membranes

Virus active on hard surfaces for 48 hours
 3. “Aerosol” spread:

Unusual but possible in very crowded
conditions
WHO Classification of Pandemic Phases
H5N1 Avian Flu – where is it now?
•
Human infections (as at 8 May 2006):
–
–
–
–
–
–
–
–
–

Turkey
Vietnam
Indonesia
Cambodia
Thailand
China
Iraq
Azerbaijan
Egypt
(12 cases, 4 deaths)
(93 cases, 42 deaths)
(33 cases, 25 deaths)
(6 cases, 6 deaths)
(22 cases, 14 deaths)
(18 cases, 12 deaths)
(2 cases, 2 deaths)
(8 cases, 5 deaths)
(13 cases, 5 deaths)
Prevention
and control of
Avian Flu
Vaccines: the first line of defence
Annual influenza vaccination is now
recommended for the following groups
• persons at high risk for influenza-related complications
• persons who live with or care for persons at high risk
• health-care workers.
Depopulation of farms and markets
PILLARS OF THE STRATEGY
• Preparedness and Communication
• Surveillance and Detection
• Response and Containment
H7N9
Influenza A(H7N9) is one of a
subgroup of influenza viruses
that normally circulate among
birds. Until recently, this virus
had not been seen in people.
However, human infections
have now been detected.
Courtesy of WHO Collaborating Centre for
Reference and Research on Influenza,
National Institute of Infectious Diseases, Japan
The disease is of concern
because most patients have
been severely ill. There is no
indication thus far that it can
be transmitted between
people, but both animal-tohuman and human-to-human
routes of transmission are
being actively investigated.
Dr Margaret Chan
Director-General
of WHO
Disease Outbreak News
Hong Kong Quarantines 19 People
After Second Case of H7N9
 Hong Kong health
officials have quarantined
19 people who had
contact with an 80-yearold man confirmed to
have the city’s second
case of H7N9 influenza,
which has killed 45
people in China this
year.
Bloomberg news Dec 8, 2013
SARS
Pandemic Influenza is different to SARS
•
•
Many institutions are using their SARS plan as the basis for their
pandemic influenza plan.
But SARS is different to pandemic influenza:
SARS
Pandemic Flu
One off unexpected event
Recurring event
Difficult to catch
Easy to catch
People only infectious when they
are symptomatic
People are infectious before they
are symptomatic
Several thousand cases, epidemic
lasted several months
Potentially millions of cases,
pandemic could last more than a
year
Easy to contain an outbreak
Almost impossible to contain an
outbreak
咳
嗽
禮
節
Thank You